SIP Trunk vs Hosted PBX: Which Does Your Australian Business Need? (2026)

The most common confusion when businesses start evaluating VOIP: they see "SIP trunk" and "cloud phone system" as two options for the same thing. They are not. A SIP trunk is the connection between your phone system and the phone network. A cloud phone system is the phone system itself. Most businesses need both, and the question is which provider supplies each component, and whether those components are bundled or separate.

This guide explains what each is, what each costs, and how to know which combination makes sense for your business.

Quick Verdict

What a SIP Trunk Is

A SIP trunk is a virtual phone line that connects a PBX (Private Branch Exchange) to the public telephone network via the internet. The word "trunk" is a legacy telecoms term for a connection that carries multiple simultaneous calls, as opposed to a single line. A SIP trunk replaces what used to be done with physical ISDN circuits or copper pairs.

When a staff member on your phone system calls a customer's mobile, the call travels from the PBX through the SIP trunk, via the phone line provider's network, to the mobile carrier, and to the customer's handset. The SIP trunk is the carrier leg of the call. Without a SIP trunk, your PBX can handle internal calls between extensions but cannot connect to external numbers.

SIP trunks are sold on a per-channel basis (concurrent call capacity) by Australian providers including Telnyx, Maxotel, Symbio Networks, Telstra Wholesale, Vonex, and others. For a comparison of Australian phone line providers and their pricing, see our phone line providers guide.

What a cloud phone system Is

A cloud phone system is a phone system (the PBX component) that runs on a provider's servers, not your own hardware. It manages extensions, ring groups, IVR menus, call queues, voicemail, and all the internal routing logic for your business's calls. Staff connect to it using IP desk phones, softphones on computers, or mobile apps.

The "hosted" in cloud phone system means you are not responsible for the server, the operating system, the software updates, or the infrastructure. The provider manages all of that. You pay a monthly fee per user or per system, and the provider ensures the PBX is running.

Critically: a cloud phone system still needs a connection to the phone network to make and receive external calls. That connection is either a SIP trunk (supplied separately) or is bundled with the cloud phone system by the same provider. This bundled model is where the confusion begins.

The Bundled vs Unbundled Distinction

Australian cloud phone system companies offer their services in two models:

• Bundled (all-in-one): The provider supplies the PBX and the SIP trunk connectivity in one product. You pay a single monthly fee per user (typically $25 to $60/month) and get a complete phone system with external calling included. Maxotel, 8x8, RingCentral AU, and Microsoft Teams Phone (via calling plans) work this way. You do not need to separately manage a SIP trunk because the provider handles the connection to the phone network internally.
• Unbundled (bring your own trunk): The provider supplies the PBX software only (3CX, FreePBX, Asterisk) and you connect it to a SIP trunk of your choice. You manage two relationships: the PBX platform and the SIP trunk carrier. This gives you more flexibility to choose the best-priced carrier for your call volume, but requires more configuration knowledge and means two vendors to manage when something goes wrong.

Most Australian SMBs choosing a cloud phone system for the first time use the bundled model. It is simpler, the pricing is predictable, and there is one provider to call when something is not working.

Direct Cost Comparison

For a 10-person business, the bundled cloud phone system model typically costs $250 to $600 per month all-in. The unbundled model (3CX PRO self-hosted on a VPS with a separate SIP trunk) typically costs $100 to $180 per month excluding hardware. The cost gap is significant at 10 users and grows with scale. The trade-off is configuration complexity and dual-vendor management in the unbundled model.

For a deeper dive into cloud phone system pricing specifically, see our cloud phone system pricing guide.

Who Should Choose Bundled cloud phone system

The bundled model suits:

• Businesses with no IT support. If you cannot configure a SIP trunk, set up a VPS, or troubleshoot a SIP registration error, the bundled model is the right choice. The provider handles the entire stack.
• Businesses with under 10 staff. At small scale, the per-user cost premium of a bundled service is worth the simplicity.
• Businesses that prioritise uptime and support SLAs. Bundled providers include managed infrastructure and support in the subscription. If the PBX goes down, you call one number.
• Businesses new to VOIP. The bundled model is the right starting point. If you outgrow it or want more control, you can migrate to an unbundled model later with more experience.

Who Should Choose SIP Trunk + Separate PBX

The unbundled model suits:

• Businesses with 10 or more staff and in-house or outsourced IT support. At scale, the cost savings are meaningful and justify the management overhead.
• Businesses with specific carrier requirements. Some industries need specific Australian carriers for call quality, pricing, or regulatory reasons. Unbundled gives you freedom to choose.
• Businesses that need advanced PBX features. Self-hosted 3CX or FreePBX offer customisation depth that most bundled cloud phone system companies do not, including complex multi-site call flows, custom integrations, and fine-grained dial plan control.
• Businesses with multiple sites. Managing a single self-cloud phone system across multiple locations with site-specific SIP trunks can be more cost-effective than per-user pricing across all locations on a bundled plan.

For a comparison of leading Australian cloud phone system companies in the bundled model, see our best cloud phone system companies guide.

Porting Your Number: How It Works in Both Models

If you are switching from a legacy PSTN or ISDN line to either a bundled cloud phone system or a separate SIP trunk setup, you will almost certainly want to port your existing geographic numbers and any 1300 or 1800 numbers to the new provider.

In the bundled cloud phone system model, the provider manages the port on your behalf. You supply the number, the existing carrier details, and any authorisation codes required, and the provider coordinates the transfer. The number is ported into the bundled service directly.

In the unbundled model, the phone line provider manages the port for the geographic numbers that route over their trunk. Your 1300 number carriage service provider may be separate again. You are coordinating two or three separate porting processes, each with its own timeline (typically 3 to 10 business days per number or batch).

If you have multiple numbers across both models (e.g., some staff on a bundled cloud phone system and one branch on a self-hosted 3CX), the porting logistics become more complex. Plan the porting sequence before any migrations begin. A number that is in mid-port cannot usually be transferred again until the first port is complete.

What Most Businesses Get Wrong

Buying a SIP trunk before having a PBX to connect it to. A SIP trunk on its own does nothing. It needs a PBX at one end to manage calls, route them to extensions, play IVR menus, and handle all the internal logic. Businesses that purchase a SIP trunk assuming it is the complete phone system solution are missing the PBX layer. If you want a complete phone system with no separate components to manage, choose a bundled cloud phone system.

Choosing a bundled cloud phone system and then trying to swap in a cheaper SIP trunk. Bundled cloud phone system services route calls through the provider's own network. You cannot usually bring a third-party SIP trunk to a bundled service. The carrier component is built into the product. If carrier flexibility is important to you, choose the unbundled model from the start.

Evaluating cost based on the SIP trunk or PBX component alone. A cheap SIP trunk from an overseas provider may have poor Australian call quality, high mobile termination rates, or no local support when something breaks. A cheap PBX licence means nothing if the SIP trunk costs are high. Always calculate the total monthly cost including both components and all expected call volumes before comparing options.

Australian-Specific Considerations

1300 number connectivity. If your business has a 1300 or 1800 number, that number is managed separately through ACMA and your carriage service provider. A bundled cloud phone system typically supports connecting your 1300 number to the system. In the unbundled model, your phone line provider needs to be configured as the carriage service provider for your 1300 number, which some phone line providers support and others do not. Confirm 1300 number support before choosing a phone line provider.

000 emergency call handling. All Australian phone systems, including VOIP, must support 000 emergency calling. In the bundled model, the provider handles 000 compliance. In the unbundled model, confirm that your phone line provider passes 000 calls correctly and that your registered address for emergency location purposes is accurate in the provider's system.

Data residency. If your business has data residency requirements (legal, government, medical), confirm where the cloud phone system company stores call recordings and metadata. Some Australian cloud phone system companies use international data centres by default. If this is a concern, choose a provider with Australian data residency or a self-hosted deployment in an Australian data centre.

Your Next Steps

To decide between bundled cloud phone system and the unbundled SIP trunk + separate PBX approach:

1. Assess your technical capability honestly. If you cannot configure a SIP trunk or manage a VPS, start with a bundled cloud phone system.
2. Calculate your expected monthly cost under each model for your actual user count and call volume. The unbundled model becomes cost-effective above roughly 10 users.
3. Identify whether you have specific carrier requirements (Australian data residency, 1300 number support, volume-based rates). If yes, the unbundled model gives you more flexibility.
4. Decide who manages the phone system on an ongoing basis. If it is you or a non-technical admin person, bundled is safer. If it is an IT provider, the unbundled model is viable.
5. Start with the simpler option and migrate later if needed. A bundled cloud phone system migration to a self-hosted system is feasible once you understand your requirements better.

If you are uncertain which model fits, the recommendation is to start with a bundled cloud phone system trial before committing to either a self-hosted deployment or a long-term bundled contract. Most Australian cloud phone system companies offer 14 to 30 day trial periods with no porting required. Use the trial to validate call quality and feature fit before making the architecture decision.

The SIP trunk vs cloud phone system decision sits within the broader question of what kind of phone system is right for your business size and technical capability. Our guide to the best phone system for small business Australia covers the full decision landscape, from simple cloud phone system to SIP trunk plus self-cloud phone system, with cost comparisons and AU provider recommendations for each model.

The SIP trunk vs cloud phone system comparison sits within the broader shift Australian businesses are making from legacy PSTN and ISDN lines to internet-based telephony. Our guide to VOIP vs traditional phone in Australia covers the full cost and reliability comparison, including where SIP trunking with a self-cloud phone system beats both legacy systems and bundled cloud phone system on total cost over 3 years.