ATA Adapter for Analogue Phones: Connect Your Existing Handsets to VOIP

This guide covers ATA adapters, what they are, how they work with Australian NBN-connected VOIP services, which models are commonly available in Australia, and when they make sense for your business. Need to Know Comms is an independent Australian publishing project with direct experience in VOIP deployment across NBN connection types and ISP infrastructure. If you've ever plugged a phone into the green port on your NBN modem and wondered why you can't connect a new Yealink or Grandstream handset to the same service, this guide is exactly what you need to read. You're not behind. The industry made this confusing on purpose.

What Is an ATA Adapter?

An Analog Telephone Adapter (ATA) converts analogue telephone audio into encoded digital media, typically transported using RTP, while SIP handles call setup and control. In plain English: it lets an old phone plug into a modern VOIP service.

Analogue phones use a physical audio connection (the RJ11 phone jack, also called an FXS port). VOIP services use SIP protocol over an internet connection. An ATA sits in between, bridging the two worlds. You connect the ATA to your router via Ethernet, plug the analogue phone into the ATA's phone port, and configure the ATA with SIP credentials from your business phone company.

ATAs have been around since the early 2000s and have been critical infrastructure for VOIP migration worldwide. In the Australian context, they matter for two distinct reasons: migrating existing office handsets to a new VOIP service, and the widespread but poorly understood ISP ATA situation that affects hundreds of thousands of Australian businesses on NBN.

The Two Very Different ATA Situations in Australia

Situation 1: The ISP-Supplied ATA (The Green Port Trap)

When NBN was rolled out across Australia, ISPs needed a way to deliver phone service to customers who had been on copper landlines. Many providers delivered NBN voice through an ATA built into their supplied modem/router, while some FTTP services used an NTD UNI-V port and other services used different arrangements. That ATA is represented by the green phone port on the back of your modem. Plug any analogue phone into that green port and it rings and dials. Most users assume this is just "how phones work on NBN".

What's actually happening: the ISP configured the built-in ATA with their own VOIP credentials. The ISP controls the SIP server, the SIP username, the SIP password, and the phone number. You don't have access to any of this. You cannot take those credentials and use them with a different business phone company. A SIP desk phone cannot connect through the analogue FXS port. Whether it can register directly to the ISP's VoIP service depends on whether that ISP supplies usable SIP credentials and supports BYO devices. You are renting the phone service from the ISP, and the ISP's ATA is the gatekeeper.

This is the green port trap. Businesses on ISP ATAs are on a VOIP service they don't control, can't customise, and in many cases can't easily leave (number porting from ISP ATA services can be difficult or impossible for some configurations). Basic ISP voice services may offer fewer hosted-PBX features than a dedicated business platform, but available functions vary by ISP and plan.

Situation 2: A Standalone ATA You Actually Control

A standalone ATA is a separate device, not built into the modem, that you purchase and configure yourself (or have your business phone company configure). It connects to your router via Ethernet and has one or more phone ports (FXS ports) for analogue handsets. You enter the SIP credentials from your chosen business phone company into the ATA's web interface, and the analogue phone connected to it registers with your VOIP service.

This is the correct use of an ATA for business. You choose the business phone company. You own the ATA device. The phone number is registered to you. You can use the same business phone company's features (ring groups, IVR, call recording) just as if you were using a native SIP desk phone, A basic analogue handset generally lacks dedicated BLF and programmable line keys. Caller ID and hook-flash transfer may work when supported by the handset, ATA configuration and VoIP platform. It's a phone call in, phone call out device.

Popular ATA Models Available in Australia

Grandstream HT models are currently available in Australia, while Cisco SPA112/SPA122 units are legacy products that may still appear in existing installations or secondary markets. Grandstream HT units are sold by Australian retailers and support standard SIP features, but compatibility and provisioning support should be confirmed with the chosen provider. Cisco SPA units appear frequently in legacy enterprise deployments.

Grandstream HT801, Single-Port Entry Level

The current one-port revision is the Grandstream HT801 v2; the original HT801 may still be available, so verify the exact SKU and revision when buying. It provides a single FXS port for one analogue phone. Configuration is through a simple web interface accessible from the same network. It supports G.711, G.729, G.722 and G.726, but compatibility must still be confirmed with the chosen provider because SIP credentials, authentication, provisioning and dial-plan requirements vary. The HT801 is the right choice if you have one analogue phone or fax machine to connect and nothing more. At around $65 AUD as at September 2026, it is the lowest barrier to testing an analogue phone on a VOIP service.

Grandstream HT802, The Most Common Business ATA in AU

The HT802 is a two-port ATA intended for residential and office environments. Two FXS ports allow two analogue devices, most commonly a desk phone on port 1 and a fax machine on port 2. The two FXS ports can be configured independently, but separate registrations, extensions and DID routing depend on the provider and PBX configuration. Both the HT801 and HT802 support T.38 fax relay and automatic G.711 fax pass-through. At around $79 AUD as at September 2026, the HT802 represents excellent value for businesses migrating two existing analogue lines to VOIP.

Grandstream HT814, Multi-Port for Larger Analogue Deployments

The current HT814 v2 provides four FXS ports; the original HT814 may also remain available, so verify the exact revision when buying. It supports G.711, G.722, G.729, G.726, and T.38 fax, and adds support for provisioning via DHCP option 66 or a provisioning server, useful if a business phone company manages the configuration centrally. At around $148 AUD as at September 2026, the HT814 is cost-effective for connecting 3-4 analogue phones to a VOIP service during a migration period. Note: for long-term use with 4 phone users, investing in 4 dedicated SIP desk phones ($80-130 each) often makes more sense than one HT814, as SIP phones deliver better call quality and features per seat.

Cisco SPA112, Enterprise-Grade 2-Port ATA

The Cisco SPA112 is a legacy two-port ATA associated with Cisco's former Linksys product lineage; Cisco acquired Linksys in 2003 and sold the Linksys business to Belkin in 2013. Its published codec set is narrower than the set listed for the Grandstream HT801/HT802. It has robust QoS marking for DSCP, which is relevant in networks with managed QoS policies. The SPA112 is often found in legacy deployments migrated from Cisco Call Manager environments. The SPA112 is an end-of-life product: Cisco ended sales in 2020 and all support in 2025. Treat it as legacy equipment rather than a current business purchase recommendation.

How to Set Up a Standalone ATA for VOIP

Setting up a Grandstream HT802 (or similar ATA) with a business phone company follows the same basic steps regardless of provider:

1. Connect the ATA to your router: Ethernet cable from the ATA's LAN port to any available port on your router or network switch. The ATA will obtain an IP address via DHCP.
2. Connect the analogue phone to the ATA: Use a standard RJ11 phone cable from the phone to the ATA's Phone 1 port (or Phone 2 for the second device on an HT802).
3. Find the ATA's IP address: Log into your router's DHCP client list to find the IP address assigned to the ATA, or use a network scanner.
4. Access the ATA web interface: Open a browser and go to the ATA's IP address (e.g., http://192.168.1.105). Default credentials are usually admin/admin (change these).
5. Enter SIP credentials from your business phone company: Navigate to the FXS Port settings. Enter the SIP Server address, SIP Username, and SIP Password provided by your business phone company. Also set the SIP User ID and Authenticate ID (usually the same as username).
6. Save and reboot: Apply settings and reboot the ATA. Within 30-60 seconds, the phone line should be active.
7. Test: Lift the analogue handset and listen for a dial tone. Dial a mobile number to confirm outbound calls work.

Most business phone companies supply specific ATA configuration guides for Grandstream HT series devices, ask for these during onboarding. If your provider doesn't offer ATA setup guidance, that's a signal to look for a more hands-on provider.

When an ATA Makes Sense for Your Business

An ATA is the right tool in three specific situations:

During VOIP Migration: Keeping Existing Phones

If your office has confirmed analogue handsets, an ATA can provide a migration bridge. Check each model first: many Avaya and Nortel handsets are proprietary digital or IP phones and will not work on an ATA's FXS port. Rather than replacing every handset on day one, you can deploy one ATA, connect your existing phones, and start using the VOIP service immediately. Then replace handsets incrementally as they fail or as budget allows. See the landline to VOIP migration guide for the full transition workflow.

Fax Machines on VOIP

Fax machines are analogue devices and cannot connect to a VOIP service directly. An ATA with T.38 fax passthrough support (the Grandstream HT802 and HT814 both support T.38) allows a fax machine to send and receive faxes over an IP network. T.38 is the standard for fax over IP and significantly improves fax reliability compared to passing fax tones through a standard voice codec. Not all business phone companies support T.38, confirm this before deploying a fax on VOIP. If fax is business-critical (legal, medical, property), verify T.38 support explicitly with your provider rather than assuming it works.

Lift Phones, Fire Panels, and Emergency Lines

Buildings with lifts, fire alarm panels, EFTPOS diallers (older models), and duress buttons often have analogue phone lines running to these devices. When transitioning a building's phone infrastructure from copper to VOIP, these legacy analogue connections need a bridge. Do not assume a standard ATA is suitable for a lift phone, monitored fire alarm, duress device or other safety-critical service. Use a solution approved by the equipment and monitoring providers, designed for service continuity, and tested after installation. Important caveat: lift emergency phones and fire panel diallers have specific regulatory requirements (AS 1735 for lifts, AS 1670 for fire systems). Confirm with the equipment supplier that VOIP-via-ATA meets the relevant Australian Standard before deploying. Some building certifiers and fire protection engineers require certified copper line emulation rather than standard VOIP ATAs for these applications.

When an ATA Does NOT Make Sense

ATAs are a bridge solution, not a destination. There are several scenarios where an ATA is the wrong tool:

• As the permanent main business line: Basic analogue phones generally lack dedicated BLF and programmable line keys. Caller ID, attended transfer and feature-code access may still work when supported by the handset, ATA configuration and VoIP platform. If this is your front desk phone, invest in a proper SIP desk phone.
• When call quality is the priority: Audio quality depends on the analogue handset, ATA, codec, network and configuration. A native SIP phone may offer better microphones, speakers and wideband implementation, but an ATA is not inherently guaranteed to produce noticeably worse calls. If your team spends significant time on calls, native SIP handsets deliver better audio.
• When you are scaling beyond 4 seats: Configuring and maintaining multiple ATAs across a growing team becomes operationally messy. At 5+ seats, standardising on SIP desk phones that are provisioned and managed centrally through the business phone company is simpler, more reliable, and easier to support.

Australian Businesses: What You Need to Know About ATAs

The NBN Silent Migration: Most AU Businesses Are on ISP ATAs Without Knowing It

Many Australian fixed-voice services now use NBN-based VoIP, but available public data do not establish how many business customers use modem-integrated ATAs or whether their migration was inadequately disclosed. The phone kept working. The number stayed the same. Nothing obviously changed. But the underlying technology changed completely, and most businesses were not told they were now on a VOIP service rather than a copper line.

Most legacy fixed-line copper services in the NBN fixed-line footprint were progressively disconnected, but exceptions remain, including some Fixed Wireless, Sky Muster, business, Special Service and non-nbn network arrangements. The choice now is: stay on the ISP ATA (limited, ISP-controlled) or move to a dedicated VOIP service (full-featured, operator-controlled).

See the PSTN shutdown guide and VOIP vs traditional phone comparison for context on how Australian telephony arrived at this point.

Power Outage: ATAs Die When the Power Goes Out

Traditional copper landlines worked during power outages because the copper pair carried power from the telephone exchange. NBN connections, and anything connected via ATA, do not. Without working battery, UPS or mobile backup, the powered equipment used by the service-such as an NTD where present, router and ATA-will stop operating during a premises power outage. Your analogue phone connected to the ATA is silent.

For businesses where telephone availability during power outages is important (medical practices, emergency response, businesses in areas with unreliable power), mitigation options include: a correctly sized UPS covering every required powered component, with runtime calculated from the combined load and required outage duration; and VOIP platform call diversion rules that redirect calls to a mobile number if the VOIP device fails to register. Both should be considered together. See the NBN VOIP setup guide for power resilience recommendations.

000 Emergency Calling via ATA

Calls to 000 from a VOIP line (including a phone connected via ATA to a proper VOIP service) are transmitted through the business phone company's infrastructure to the emergency call handler. Confirm that the chosen VoIP service supports 000. ACMA says 000 is available from certain VoIP services, while the applicable provider obligations depend on the regulated service being supplied. However, unlike copper landlines where your physical address is automatically transmitted to emergency services, VOIP 000 calls rely on a registered service address that you must provide to your business phone company. If the registered address does not match where the call is being made from (e.g., a remote worker using a softphone or a business that has moved premises without updating the service address), emergency services may dispatch to the wrong location. Always register and update your service address with your business phone company, and make this part of onboarding for any new phone deployment including ATA-connected phones.

Can You Port the Number from Your ISP ATA?

In most cases, yes, but it depends on how the ISP has provisioned the service. Geographic numbers (02, 03, 07, 08) assigned to an ISP ATA service are generally portable under ACMA's local number portability rules. The receiving business phone company initiates the port on your behalf. The ISP (as the losing carrier) is required to release the number within the regulated process; individual local-number ports generally take 8 to 15 business days, while complex ports may take up to 30 business days.

Porting can still be affected by request validation, whether the number remains active, the gaining provider's acceptance and the complexity of the port. Contract exit fees may apply separately but do not give the losing telco a right to withhold an otherwise valid port.

Before committing to a new business phone company, ask them to initiate a porting feasibility check on your existing number. Reputable providers will do this before you sign, not after. See the guide on hidden VOIP costs for porting gotchas to watch for.

NBN Call Quality: ATA vs Native SIP Phone

NBN connection quality varies significantly by technology type and distance from the node. On a solid FTTP or HFC connection with a quality router and QoS configured, VOIP call quality through an ATA is generally excellent, G.711 codec, full 64kbps audio, comparable to a copper landline. On an FTTN connection with a long copper run (high attenuation), or on a congested HFC network during peak hours, call quality can degrade: jitter, packet loss, and dropped calls become more common.

Both ATAs and SIP phones may implement jitter buffers; their effectiveness is model- and firmware-specific and should not be inferred solely from the device category. A Yealink T54W, for example, has an adaptive jitter buffer that compensates for network variability. An analogue handset connected to a Grandstream HT802 relies on the ATA's simpler jitter buffer. The practical difference is small on a well-provisioned network and more noticeable on marginal connections.

Check the VOIP call quality guide for a full breakdown of NBN-specific quality factors.

What Most Businesses Get Wrong About ATAs

Mistake 1: Buying a New SIP Phone and Trying to Plug It Into the Green Port

This is the most common and most frustrating mistake. A business owner reads about VOIP, decides to upgrade from the basic analogue handset on the NBN modem, and buys a Yealink T31P or Grandstream GXP1625. They plug it into the green phone port on the NBN modem. Nothing happens. The phone won't register. The business owner calls the ISP, who says "we don't support third-party devices". The phone gets returned.

What went wrong: the green port on the NBN modem is not a SIP-accessible port. It is an analogue FXS port connected to the ISP's own ATA. A SIP phone cannot register with the ISP's VOIP credentials because those credentials are locked to the modem and not exposed. The SIP phone needs its own VOIP service, a separate account with a business phone company (not the ISP), and connects to your network via Ethernet, not via the green port. The green port is for analogue phones only.

Mistake 2: Using an ATA as a Long-Term Solution for the Main Business Line

An ATA is an excellent migration tool and a practical solution for fax and legacy devices. It is not an ideal long-term solution for the primary business phone line. Basic analogue phones usually lack dedicated BLF and multiple line-appearance keys. Attended transfer and other feature-code functions may still be available when supported by the ATA, handset and VoIP platform. For the front desk or the primary inbound line, a proper SIP desk phone delivers a fundamentally better experience for both staff and callers. The best SIP desk phones guide covers entry-level options starting at $80 AUD that outperform any ATA-connected analogue handset in business use.

Mistake 3: Not Checking Whether the ISP ATA Number Can Be Ported Before Signing With a New Provider

Businesses that want to move from their ISP ATA to a proper VOIP service sometimes sign a contract with a new business phone company, only to discover during the porting process that their number has a complication, tied to a bundled plan with exit fees, or provisioned in a way that makes the port take 3-4 weeks instead of 5 business days. By this point, they are committed to the new provider and dealing with the porting problem from a position of less leverage. The fix: ask the new provider to run a porting feasibility check before you sign. Take 10 minutes to confirm the port is straightforward. If it is not, understand exactly what the delay or cost will be before committing.

Your Next Steps: Choosing the Right Path

Use this checklist to determine the right approach for your business:

• Check what's plugged into your NBN modem right now: If your phones connect to the green port on the modem, you are on an ISP ATA. Make a note of which ISP and what number.
• Decide whether to keep analogue phones or replace them: If existing phones are less than 3-4 years old and in good condition, an ATA bridge during migration is reasonable. If they are older than 5 years or basic unbranded handsets, budget for SIP replacements.
• Check porting feasibility for your number: Contact a business phone company and ask them to run a porting check before you commit.
• Choose a business phone company that supports ATA configuration: Not all do. Confirm the provider supplies SIP credentials compatible with Grandstream HT series ATAs.
• For fax machines: Confirm your chosen provider supports T.38 before deploying fax on VOIP.
• Plan for power resilience: If phone availability during outages matters, budget for a UPS covering the NBN NTD, router, and ATA.
• Verify 000 address registration: Once live on the new VOIP service, confirm your service address is correctly registered.

Not sure which setup is right for your team? Use the phone system sizing wizard to get a personalised recommendation, or get a free recommendation from the Need to Know Comms team.

ISPs often bundle a basic ATA (Analog Telephone Adapter) with NBN services to replace the copper landline. This is technically VOIP but lacks the routing, call management, and redundancy features a business needs. Our guide covers ISP phone services for business in Australia, including the features you are missing and what an upgrade actually costs.

Not every ATA adapter works seamlessly with every phone line provider, codec support, SIP registration methods, and NAT traversal handling all vary by model. Our Phone Compatibility Checker covers common ATA models and assesses their compatibility with major Australian business phone companies.

What Does an ATA Adapter Cost?

Australian ATA pricing varies by port count, revision, retailer and stock status; check current pricing for the exact model rather than applying one range to all units. As at September 2026, our nightly Australian price tracking records the Grandstream HT801 (single port, one analogue phone) at around $65, the HT802 (two ports) at around $79, and the HT814 (four ports) at around $148. These are cheapest-listing figures and move with stock. The HT812 has two FXS ports, the HT814 has four, and the HT818 is the eight-port model. These are one-off hardware costs. Ongoing cloud-phone costs vary by provider, licence structure, call inclusions and optional features; compare the chosen provider's current plan and call charges. An ATA setup typically costs less upfront than replacing all existing handsets with new SIP phones, provided the existing analogue phones are in good working condition.

What is an ATA adapter and why would I need one for my business?

An ATA (Analog Telephone Adapter) converts the audio signal from a traditional analogue phone into digital SIP data that can travel over an internet connection. You would need one if you want to connect existing analogue handsets (Panasonic, Uniden, or other corded desk phones) to a modern VOIP service without replacing the physical phones. ATAs are also used to connect fax machines, lift phones, and fire panel diallers to IP networks.

Can I use a Yealink or Grandstream SIP phone with the green port on my NBN modem?

No. The green phone port on an NBN modem is an analogue FXS port connected to an ISP-controlled VOIP service. A SIP desk phone cannot register through the analogue FXS port. Direct registration to the ISP service is possible only where the ISP supplies compatible SIP credentials and permits BYO devices. A SIP phone like the Yealink T31P needs its own VOIP service account (from a provider like Maxotel or similar) and connects to your network via Ethernet, not via the green port. The green port is for analogue phones only.

What is the difference between an ISP-supplied ATA and a standalone ATA?

An ISP-supplied ATA is built into your NBN modem and configured by your ISP with their own VOIP credentials. You don't control the service, the credentials, or the call features. A standalone ATA is a separate device you purchase (like the Grandstream HT802) and configure with SIP credentials from a business phone company of your choosing. With a standalone ATA, you own the service, choose the provider, and can access full VOIP features (IVR, ring groups, call recording). The standalone ATA is the tool that lets you escape the ISP ATA lock-in.

Which ATA adapter should I buy for my small business in Australia?

For a current two-port purchase, check the Grandstream HT802 v2 and confirm the exact revision, provider compatibility and current Australian price. It provides two ports (one phone, one fax), supports all major codecs including T.38 for fax passthrough, is widely compatible with Australian business phone companies, and has a straightforward web configuration interface. If you only need one port, the HT801 (~$65) is sufficient. If you need four ports, the HT814 (~$148) covers a small office with multiple analogue lines. Both figures are as at September 2026. Grandstream HT units are available from Scorptec, PLE Computers, and various AU business IT distributors.

Does an ATA work for fax machines in Australia?

Yes, with caveats. ATAs with T.38 fax passthrough support (including the Grandstream HT802 and HT814) allow fax machines to send and receive over VOIP. T.38 is the recommended standard for fax over IP, it encapsulates fax signals more reliably than passing raw fax tones through a voice codec. Before deploying fax on VOIP via ATA, confirm your business phone company supports T.38. If your fax use is business-critical (legal or medical practice), verify with the provider that T.38 is supported end-to-end and test a few fax transmissions before relying on it operationally.

Can I port my phone number from an ISP ATA to a new VOIP service?

In most cases, yes. Geographic numbers (02, 03, 07, 08) assigned to ISP ATA services are generally portable under ACMA's local number portability rules. The new business phone company initiates the port on your behalf and the ISP must release the number through the regulated process; individual local-number ports generally take 8 to 15 business days, while complex ports may take up to 30 business days. However, some ISPs have provisioned numbers in ways that complicate porting, tied to bundled contracts, allocated from non-standard blocks, or with slow port-out processes. Always ask your new provider to run a porting feasibility check before signing a contract, not after.

Does an ATA-connected phone work during a power outage?

No. Unlike traditional copper landlines (which carried power from the telephone exchange), ATA-connected phones stop working when the power goes out. The ATA needs power to operate, and the NBN NTD and router also need power for the network connection to be available. For businesses where phone availability during outages is important, mitigation options include a UPS (uninterruptible power supply) for the NBN NTD, router, and ATA, providing 30-60 minutes of backup power, and call diversion rules in your VOIP platform that redirect calls to a mobile number if the VOIP devices fail to register.