Quick Summary: Cat A vs Cat C at a Glance
| Category A (Simple) | Category C (Complex) | |
|---|---|---|
| Typical number types | Single geographic number (02/03/07/08 prefix) associated with a simple telephone service | ISDN services, number blocks, multi-carrier services, technology crossover |
| Standard timeline | 8 to 15 business days (80% within 8 days, 98% within 15) | 15 to 20 business days (up to 30 in complex cases) |
| Best case | 80% complete within 8 business days | 80% complete within 15 business days |
| After one rejection | Add 8 to 15 business days (port restarts) | Add 15 to 20 business days (port restarts) |
| Coordination required | Gaining and losing carrier only | May involve multiple carriers, manual coordination |
| Regulatory framework | ACMA Numbering Plan, LNP automated system | ACMA Numbering Plan, manual carrier coordination |
| 1300/1800 numbers | Not applicable (different process entirely) | Not applicable (Smart Numbers database transfer) |
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Your provider can tell you which category applies to your specific number before you submit anything. This should be one of the first questions you ask during onboarding. If they give you a timeline without specifying the category, ask directly: 'Is this a Category A or Category C port?' The category determines whether you have days or weeks to plan around.
What Is Category A Porting?
Category A is the simple port. It commonly covers a single geographic number associated with a simple telephone service. Mobile numbers use the separate Mobile Number Portability framework. If you have an 02, 03, 07, or 08 prefix number and you are moving to a business phone company, there is a good chance you are in Cat A. For a comparison of current options, see our guide to the best phone system for small business in Australia.The Category A process uses the Local Number Portability (LNP) system, which is the automated carrier-to-carrier infrastructure that handles the bulk of Australian number ports. When your new provider submits a Cat A porting authority, the LNP system validates your account details against the losing carrier's billing records, schedules the cutover, and flips the number at the agreed time. The final technical activation target is 90% within 30 minutes and 99% within 2 hours after a valid ECA reaches the losing carrier. Separately, after SNA confirmation and where infrastructure exists, the gaining provider's targets are 80% within 8 business days, 90% within 10 and 98% within 15, subject to the Code's exclusions; these are not whole-process guarantees. -- so the realistic planning window is 8 to 15 business days, not the 1 to 5 days some providers quote informally.What makes a port Category A comes down to three things. First, it involves a single number, not a block of numbers. Second, the number type does not require special handling, meaning it is a standard geographic or mobile number, not an ISDN service or a multi-line group. Third, the port does not cross a fundamental technology boundary in a way that requires manual carrier coordination. Most VOIP-to-VOIP ports and most ISP ATA-to-VOIP ports for geographic numbers fall into Cat A. A simple number can occasionally still be processed as Cat C, for example when it sits within a customer group or PABX/multi-line arrangement -- the category follows the service type and coordination required, not just the number itself.
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The ISP ATA scenario deserves a specific note. Many Australian businesses currently have their phone number delivered via the green phone port on their ISP-supplied modem. That port uses an Analog Telephone Adapter to connect an analogue handset to the provider's voice service. Porting that number to a real business phone company is typically still a Category A port, because the number itself is a standard geographic number. The technology change is at the endpoint, not at the carrier level. Your new provider will confirm this when they check your number in the LNP database.
Category A Timeline: What Actually Happens
Day 1: Your new provider submits the porting authority form to the LNP system on your behalf. The losing carrier receives a notification.The losing carrier validates the Cat A request and must confirm or reject 99% of SNAs within one business day. The current Code's validation criteria concern matters such as number status, pending orders and whether the number is associated with a simple telephone service. If anything does not match, it is rejected at this stage and the clock resets.After confirmation, the gaining provider arranges the cutover timing with the customer; available dates and appointment windows vary by provider and carrier. The cutover is booked.Cutover day: During the nominated window, your number flips from the old system to the new one. The Code's Cat A activation targets are at least 90% within 30 minutes and at least 99% within two hours after receipt of a valid ECA during standard hours. During this window, call routing is in transition. Schedule your cutover during your lowest call volume period.After cutover: Your number is live on the new VOIP system. Test an inbound call immediately. If it lands on your new system, the port is complete. Your old service can now be cancelled. Not before.What Is Category C Porting?
Category C is the complex port. It applies when the port involves circumstances that cannot be handled entirely through the automated LNP system. Category C ports require additional manual coordination between carriers, and sometimes between multiple carriers, which is why the timeline is longer and less predictable.Cat C is not rare, but it is less common than Cat A for typical small business migrations. The scenarios that trigger Category C are specific, and it is worth knowing them before you assume your port is straightforward.What Triggers Category C
Cat C is used where the number is associated with a complex telephone service or the port requires manual processing coordination; legacy ISDN services are a common example cited by providers. If your current service is on a legacy ISDN circuit (ISDN2 or ISDN10/20/30), moving that number to a VOIP service crosses a technology boundary that requires manual decommissioning on the losing carrier's side. ISDN services cannot simply flip via the LNP system. They require the losing carrier to physically or logically decommission the ISDN service as part of the port. Most legacy fixed-line services in NBN fixed-line rollout areas have migrated, but Australia did not complete a nationwide PSTN copper shutdown in 2025; some copper voice services remain.Multi-number porting is another common Cat C scenario. If you want to port a range of geographic numbers together, rather than one at a time, the port is categorised as complex. This applies to businesses that have multiple geographic numbers on the same account and want them all to move to the new system simultaneously. Your provider can port them individually as Cat A ports over multiple requests, or as a grouped Cat C port. There are operational reasons to prefer one approach over the other depending on your cutover strategy.Multi-carrier services add complexity because the losing carrier cannot act alone. If your current phone service involves a wholesale arrangement where one carrier provides the underlying infrastructure and another provides the retail service, both carriers need to coordinate the release of the number. Your new provider may not have direct relationships with both parties. Manual coordination is required.A block or batch of associated geographic numbers ported together uses the Cat C process, although ACMA notes that a number from a group can be ported individually where the service and applicable arrangements permit. If you are porting a consecutive block of geographic numbers (for example, a range of 10 numbers used by a small call centre), the port cannot be processed individually through the LNP system. It requires a Category C process with explicit block-level coordination.Certain legacy service types on obsolete infrastructure also trigger Category C. This is less common but it happens.Category C Timeline: What Actually Happens
The Category C process follows the same general steps as Cat A, but with additional coordination stages that cannot be rushed. The gaining carrier submits the porting authority. The losing carrier acknowledges receipt. For Cat C, the losing carrier then needs to perform additional steps: de-provisioning ISDN equipment, coordinating with wholesale partners, or processing block-level changes. These steps require human scheduling, not just automated validation.Realistic Cat C timeline: 15 to 20 business days for a clean first-attempt port. Following CNA confirmation and where infrastructure exists, the Cat C targets are 80% within 15 business days, 90% within 20 and 99% within 30, subject to the Code's exclusions. These metrics are not an unconditional end-to-end upper limit. For consumer/SME Cat C ports specifically, the code notes cutovers will generally occur in under 20 business days.Cat C rejection recovery takes longer too. A corrected Cat C CNA is treated as a new notification, so a rejection can materially delay the port; the additional time varies and is not fixed at 15 to 20 business days. This is why planning buffer time is even more critical for Cat C ports.
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If you are moving from a legacy ISDN service, confirm with your new provider that they have processed ISDN-to-VOIP Cat C ports before. Most competent business phone companies have done this many times since the PSTN shutdown. If your provider seems unfamiliar with the ISDN decommissioning coordination step, that is a signal about their experience level. Ask how many ISDN-to-VOIP ports they have processed in the past 12 months.
1300 and 1800 Numbers: A Separate Category
1300 and 1800 numbers do not use the Cat A or Cat C porting framework at all. They are non-geographic numbers managed under the ACMA's Smart Numbers database and delivered via a carrier assignment model rather than a network porting model. Moving a 1300 or 1800 number between carrier networks is an inbound number port governed by the separate Inbound Number Portability Code, not by the Cat A/C local-number process.In practical terms for businesses: the process takes longer and involves different documentation. The gaining provider must obtain customer authorisation and the service account details required by the Inbound Number Portability Code. Additional provider paperwork may vary; an enhanced-rights transfer applies only when ownership or licensing of a smartnumber itself is being traded. Some providers manage this entire process on your behalf. Others hand you the forms. Confirm which approach your provider takes before you start.Timeline for 1300 and 1800 transfers: these are not Cat A or Cat C ports at all. Under ACMA's Inbound Number Portability Code, the losing carrier must respond to a transfer request within 2 business days, and the technical cutover itself is fast once approved (95% within 2 hours, 99.9% within 16 hours). The Code sets a two-business-day response requirement and technical completion targets after Port Proceed, but the total customer-facing timeframe varies with the gaining provider's verification and provisioning process. Obtain an end-to-end estimate from the provider. For full detail on how 1300 numbers work and what they cost, see our 1300 number guide.
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1300 and 1800 ports use the separate Inbound Number Portability process. Their timing depends on validation, provider provisioning and the Code's port transactions, not on Cat C classification. Do not plan a 1300 number transfer on a tight deadline. Build in 4 weeks from decision to go-live.
How to Find Out Which Category Your Port Is
You do not have to guess. Your provider can assess the likely category from the current service configuration. Definitive service information or pre-port validation may require customer authorisation and inter-carrier checks under C540. This lookup is part of standard onboarding for any competent business phone company. Ask for it explicitly if they do not volunteer the information.The provider can assess the likely category from known service details and, after obtaining valid customer authorisation, request service information or pre-port validation from the losing provider where needed. From this information, they can categorise the port and give you a realistic timeline. If they say 'we will not know until we submit', push back. They should be able to give you a category assessment before submission.There are also clues you can use to anticipate the category yourself before you speak to a provider. If you have a single geographic number that has been on a standard business VOIP or NBN phone service for the past few years, you are almost certainly Cat A. If your service dates back to a period before NBN, if you were ever on an ISDN circuit, if you have multiple numbers on one account, or if you have changed providers multiple times and are unsure of what sits behind your service, Cat C is more likely.Questions to Ask Your Provider to Determine Category
Ask your new provider these specific questions before submitting a porting authority form:Have you looked up my number in the LNP database? What does it show as the current service type? Is this a Category A or Category C port based on that lookup? What is your realistic timeline for this specific port, not the general range? If this is Category C, what is the reason and which carriers are involved? Have you done this type of port before, and what is your typical success rate on first attempt?A provider who answers these questions specifically and confidently has done this before. A provider who gives vague answers or says they need to submit first to find out is telling you something about their process. For a broader view of what switching to VOIP involves, see our VOIP vs traditional phone guide.The ACMA Numbering Plan: What the Rules Actually Say
Both Cat A and Cat C porting are governed by the ACMA Telecommunications Numbering Plan. The Telecommunications Numbering Plan 2025 establishes the high-level obligation to provide number portability. Registered industry codes set the operational procedures, service metrics and validation or rejection rules for local, mobile and inbound ports.Under the Numbering Plan, losing carriers cannot refuse a valid porting request because they want to retain your business. They are required to process valid requests within the prescribed timeframe for the category. For Cat A, 99% of SNAs must be validated and either confirmed or rejected within one business day. For Cat C, the timeframe is extended to accommodate the additional coordination steps involved.The Plan also sets out the legitimate reasons a losing carrier can reject a porting request. Valid rejection reasons are limited to the criteria in the applicable portability code, such as a disconnected number, a pending port or pending customer order, or the number being associated with a service that cannot use the submitted category. An outstanding balance cannot be used to refuse or delay the port. A losing carrier cannot reject a port because 'the customer is still in contract'. An early termination fee may be charged, but it cannot block the port.The Australian Telecommunications Alliance publishes the operational industry codes under the regulatory framework, and ACMA registers and enforces compliance with registered codes, including the Local Number Portability Code that sets out how the LNP system is used in practice. Your provider operates under this Code. If a provider is not following these procedures, that is a regulatory issue, not just a customer service issue.If a losing carrier is obstructing a valid port, the escalation path is: first, a formal complaint to the losing carrier's complaints team. Second, if that does not resolve within a reasonable timeframe, a complaint to the Telecommunications Industry Ombudsman (TIO). The TIO escalates an eligible complaint to a dedicated team at the provider; under its current process, the provider generally has up to 10 working days to propose a resolution. The TIO service is free for consumers and small businesses. More detail on rejection handling is in our number porting timeline guide.How Category Affects Rejection Handling
Port rejections work the same way for Cat A and Cat C: the losing carrier returns a reason code, your new provider communicates this to you, you correct the information, and the port is resubmitted. The difference is what the rejection costs you in time.A corrected Cat A request must be processed again, so a rejection delays the port. The added time varies; the 8/10/15-day Code metrics apply after confirmation and are not a fixed penalty for every rejection. If your original timeline was on the faster end and you receive a rejection early, you are now looking at 15 to 20+ business days total from submission.A Cat C rejection adds another 15 to 20 business days per rejection cycle. This is because the resubmission restarts the manual coordination process. Two rejections on a Cat C port can stretch the total timeline past 6 weeks.Verify the Service Account Number and all information required by the gaining provider. Rejection criteria differ by category and transaction; the current Cat A Code does not list exact account-holder-name or punctuation matching as a validation criterion. Verify the exact name before submitting.For Cat C ports specifically, there is an additional rejection scenario that does not apply to Cat A: coordination failure. This is where the losing carrier begins the decommissioning or coordination process and encounters a technical complication with the legacy infrastructure. This is relatively rare but it is specific to Cat C. Your provider should communicate clearly if this is the reason for a delay and what steps are being taken to resolve it.Planning Your Timeline Based on Category
The correct approach is to work backwards from your target go-live date, not forwards from your decision date. Most businesses do it the wrong way.For a Category A port: start by confirming the category with your provider. Add 15 business days for the port timeline (the regulated upper bound for 98% of ports). Add a similar buffer for one potential rejection. Add 10 business days to set up and test your new VOIP system on a temporary number before the port completes. Total minimum lead time from starting the process to a safe go-live date: around 6 weeks, including buffer.For a Category C port: the same structure applies but the numbers are larger. Add 20 business days for the port timeline (the regulated upper bound for 90% of ports, with a 30-day outer limit for the remainder). Add a similar buffer for one rejection cycle. Add 10 business days for system setup and testing. Total minimum lead time for a safe Cat C go-live: 8 to 10 weeks. Businesses in ISDN-to-VOIP migrations who have hard go-live deadlines should start the process well ahead of that.Your new VOIP system should be fully configured and tested on a temporary number before you submit the porting authority. When the port completes, the number lands on an already-working system. This is not optional. Businesses that submit the port and then start configuring the system create a scenario where the port completes before they are ready. For a full view of the migration process, see our landline to VOIP migration guide.Australian Businesses: What to Know Before You Start
The migration from legacy fixed-line services to NBN-based services has made porting configuration more relevant, but Australia did not complete a nationwide PSTN copper shutdown in 2025. If your business was on a traditional copper-based landline at any point in the past decade, your service has either already been migrated to an NBN-based VOIP service by your ISP, or you are overdue for the transition.The NBN migration created a specific situation that catches businesses by surprise. When the NBN was rolled out, ISPs moved customers from PSTN to VOIP via the ATA port on the NBN-supplied modem. This happened quietly, with minimal explanation to customers. The result is that many Australian businesses today have a VOIP number delivered via an ISP ATA, without knowing it. Their phone plugs into the green port on the router. They have no SIP credentials. They have no way to add features or port the number independently.For this cohort, the port may be Cat A if the number is associated with a simple telephone service. The modem's ATA port alone does not determine the category. The number is a standard geographic number on a standard NBN-based VOIP service. The complexity is the account detail verification, not the technology. Your provider will confirm this when they look up the number.The businesses more likely to be in Category C are those that have been operating on legacy infrastructure for an extended period. ISDN services were common in Australian businesses throughout the 2000s and early 2010s. If your business dates from that era and has never done a significant phone infrastructure review, there is a real chance your service has ISDN components. Ask your current provider what type of service your number is on before you engage a new provider. 'We are on NBN' is a sufficient answer for most modern services. 'We are on ISDN' or 'we have a T-series circuit' means you are in Cat C territory.Submitting Cat A for a number associated with a complex service can cause rejection; providers should assess the service configuration before submission. For the full list of rejection causes and how to resolve each one, see our guide to number porting rejection reasons in Australia.
What Most Businesses Get Wrong About Porting Categories
Mistake 1: Assuming Category A and Getting Surprised by Category C
The most expensive mistake in porting planning is assuming your port is Category A without confirming it, then building a go-live plan around the fastest-case figure some providers quote informally. If your number turns out to be Cat C, an 8-day best-case assumption becomes a 20-day-plus minimum. Businesses that have announced a go-live date to staff and customers and committed to a system launch date cannot easily absorb a two-week slip. The fix is 5 minutes at the start of the process: ask your provider to confirm the category before you plan anything around a timeline.Mistake 2: Not Verifying the Exact Account Holder Name Before Submitting
Account holder name mismatch is the leading rejection reason for both Cat A and Cat C ports. It is also entirely preventable. The fix is a 5-minute call to your current provider before submitting anything: ask them to read out exactly what appears as the account holder name in their system. Write it down character for character. If the account was set up under a former business name, a previous owner's personal name, or a legal entity name that differs from your trading name, the porting authority must use the name in the system, not the name you go by. Submit what the system has.Mistake 3: Treating 1300 and 1800 Numbers as Standard Ports
1300 and 1800 numbers are not ported through the Cat A or Cat C LNP framework. They are transferred through the ACMA Smart Numbers database via a carrier assignment process. This distinction matters because the timeline is different (allow several business days to two weeks, not the 8 to 15 business day Cat A window), the documentation is different (Right of Use transfer, not a standard porting authority), and the process is different (carrier assignment versus LNP submission). Businesses that treat a 1300 number like a standard geographic port will submit the wrong forms and add weeks to their timeline. If you have a 1300 or 1800 number, confirm explicitly with your provider that they understand it goes through the Smart Numbers process, not the standard porting system.Your Next Steps: Category Confirmation Checklist
Before submitting any porting authority, work through this checklist:[ ] Ask your new provider to look up your number in the LNP database. Get a written confirmation of whether it is Cat A or Cat C. [ ] If Cat C: ask your provider to confirm which specific factor is triggering the Cat C categorisation (ISDN, multi-number, multi-carrier, etc.) and what coordination is required. [ ] If you have a 1300 or 1800 number: confirm with your provider that they are using the Smart Numbers process, not the LNP porting framework. Get a realistic timeline in writing. [ ] Call your current provider and ask them to read out the exact account holder name as it appears in their system. Write it down. This is what goes on the porting authority form. [ ] Confirm the service identifier (SPIN or account number at the service level) for the specific number you are porting. [ ] Set your go-live date based on the confirmed category: around 6 weeks minimum for Cat A, 8 to 10 weeks for Cat C, several business days to two weeks for a 1300/1800 transfer. [ ] Set up your new VOIP system on a temporary number. Configure call routing, IVR, ring groups, voicemail. Test inbound and outbound calls. Do not submit the port until the system is ready. [ ] Choose a cutover date and time window during your lowest call volume period. [ ] Forward calls to a mobile number during the cutover window as a backup. [ ] Brief your team on the cutover date and what to expect. [ ] After the port completes and you have tested inbound calls successfully: cancel your old service.If you want guidance on which provider handles your specific porting scenario smoothly, our team can recommend based on your number type, current setup, and business size. Visit the Get a Recommendation page and tell us what you are working with.Identifying which porting category applies to your number is the first step, and it is not always obvious from the number format alone. Our Number Porting Checker classifies your number as Cat A or Cat C and explains what that means for your timeline and documentation requirements.
Do CAT-A and CAT-C Ports Cost Different Amounts?
Porting, rejection and related administration fees vary by provider, port category and batch size. Check both the gaining and losing providers' current fee schedules before submitting. Either provider may impose charges under its terms, and gaining providers commonly publish porting or rejection fees; check both providers' current schedules. Ongoing cloud phone pricing is independent of whether the number used Cat A or Cat C, but it varies by provider, call plan, devices and included features.
What is Cat A porting in Australia?
Cat A (Category A) is the simple port category under the ACMA Telecommunications Numbering Plan. It applies to individual geographic numbers (02, 03, 07, 08 prefix) and mobile numbers moving between providers using compatible network technology. Cat A ports are processed through the automated Local Number Portability (LNP) system. Under ACMA's Local Number Portability Code, 80% complete within 8 business days, 90% within 10, and 98% within 15 -- so plan for 8 to 15 business days, not the faster figures some providers quote informally. Most Australian small business VOIP migrations are Category A ports.
What is Cat C porting in Australia?
Cat C (Category C) is the complex port category. It applies when the port involves a technology crossover (such as moving from an ISDN service to VOIP), when multiple numbers are being ported together in a block, when multiple carriers are involved in delivering the current service, or when legacy infrastructure requires manual coordination on the losing carrier's side. Cat C ports require additional manual steps beyond the automated LNP system and typically take 15 to 20 business days (up to 30 in complex cases).
How do I find out if my port is Category A or Category C?
Ask your new provider to look up your number in the LNP database before you submit a porting authority. A competent provider can tell you the current service type on your number and categorise the port based on that information. You do not have to submit anything to find out. If the provider says they cannot tell you the category until after submission, ask why. Most modern business phone companies can give you a category assessment within minutes of looking up the number.
Does porting from an ISP green port (ATA) count as Cat A or Cat C?
Porting a number from an ISP ATA service to a proper business phone company is typically Category A. The number itself is a standard geographic number, and the fact that it is currently delivered via an ISP-controlled ATA on an NBN modem does not change the port category. The category is based on the carrier-level service type, not the endpoint hardware. Your new provider can confirm this when they look up your number. The process is the same as any Cat A port: porting authority form, account detail verification, LNP submission, cutover scheduling.
Is porting a 1300 number Cat A or Cat C?
Neither. 1300 and 1800 numbers are not ported through the Cat A or Cat C LNP framework at all. They are non-geographic numbers managed in the ACMA Smart Numbers database under a carrier assignment model. Moving a 1300 or 1800 number to a new carrier is a carrier assignment transfer, not a port in the technical sense. The process requires different documentation (Right of Use transfer). The losing carrier must respond within 2 business days and the technical cutover is fast once approved, but end to end (including verification and routing setup) allow several business days to two weeks for a straightforward transfer. If your provider treats a 1300 number as a standard port, they are using the wrong process.
What makes a port become Category C instead of Category A?
The factors that trigger Category C are: the service is on an ISDN circuit (ISDN2 or ISDN10/20/30) rather than a standard NBN VOIP or PSTN line; you are porting multiple numbers together as a block rather than individually; more than one carrier is involved in delivering your current service and both need to coordinate the release; or the number has legacy routing flags in the system that require manual resolution. Your provider can identify these factors by looking up the number before submission. Most single-number NBN VOIP ports are Cat A.
How long does a Cat C port take in Australia?
Category C ports typically take 15 to 20 business days for a clean first-attempt port under ACMA's regulated service levels (80% within 15 business days, 90% within 20, 99% within 30). For consumer/SME ports specifically, the code notes cutovers will generally occur in under 20 business days. A Cat C rejection adds another 15 to 20 business days per cycle. For planning purposes, allow 8 to 10 weeks from starting the process to a safe go-live date, including setup time and one rejection buffer.
Can my current provider refuse to do a Cat C port?
No. Under the ACMA Telecommunications Numbering Plan, losing carriers are legally required to support valid porting requests regardless of category. A provider can reject a port for legitimate technical reasons such as account detail mismatches, but they cannot refuse to process a valid Cat C port because the coordination is inconvenient or because they want to retain your business. If a losing carrier is obstructing a valid Cat C port, the escalation path is: formal complaint to the losing carrier's complaints team, then a complaint to the Telecommunications Industry Ombudsman (TIO) at tio.com.au if that does not resolve it. Most obstruction issues resolve quickly once a TIO reference is in play.
What is the ACMA Numbering Plan and how does it relate to porting categories?
The ACMA Telecommunications Numbering Plan is the regulatory framework that governs how phone numbers are allocated, managed, and ported in Australia. It establishes the obligation on all carriers to support number portability, sets the timeframes within which losing carriers must process ports by category, and defines valid rejection reasons. The Communications Alliance administers the operational procedures under the Plan, including the Local Number Portability Code that governs how the LNP system works in practice. When providers refer to Cat A and Cat C, they are using categories defined by this framework. The ACMA website at acma.gov.au has the full Numbering Plan for reference.
I am moving from a traditional ISDN service to VOIP. Is that Cat C?
Yes. Moving from an ISDN service (ISDN2, ISDN10, ISDN20, or ISDN30) to a business phone company is a Category C port. ISDN services cross a technology boundary that cannot be handled through the automated LNP system. The losing carrier needs to decommission the ISDN equipment and release the number through a manual coordination process. Legacy ISDN services are commonly handled as complex Cat C ports, but Australia did not complete a nationwide PSTN copper shutdown in 2025 and no authoritative source establishes this as the most common Cat C scenario. Allow 6 to 7 weeks from decision to go-live and confirm your new provider has experience with this specific migration type.
What happens to my calls during a port cutover window?
A cutover may involve a brief disruption, but its duration and call-routing behaviour vary by carrier and port. Confirm the expected window and contingency process with the gaining provider, and report failed routing rather than assuming it is normal propagation. Manage it by scheduling the cutover during your lowest call volume period (early morning or late afternoon), forwarding your number to a mobile before the window starts as a backup, and testing an inbound call as soon as your provider confirms completion. Once the test call lands on your new system, the cutover is done.
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