SIP Trunk vs Hosted PBX Australia: Which Is Right for Your Business? (2026)

The key difference is who owns the PBX. A SIP trunk delivers phone calls over the internet to a PBX system that you own and manage yourself. A hosted PBX means the provider manages everything - you pay per seat and never touch the underlying system. For most Australian SMBs under 20 seats, hosted PBX is simpler, faster to deploy, and carries less risk. But at larger scales, or when you already have an existing PBX, SIP trunks can be significantly cheaper. This guide maps out exactly where the trade-off sits.

What SIP Trunking Actually Is

A SIP trunk is a telephone line delivered over the internet using the SIP (Session Initiation Protocol) standard. It is nothing more than the call delivery layer - the pipe that carries calls in and out of your building or network. On its own, a SIP trunk does nothing. It must connect to a PBX (Private Branch Exchange) before it can ring an extension, send calls to a ring group, or route callers through a menu.The PBX is a separate system - software that manages all the routing logic for your phones. Popular self-hosted PBX platforms in Australia include 3CX, FreePBX, and Asterisk. If you have one of these running on your own hardware or a VPS, you point a SIP trunk at it and the calls flow through. The SIP trunk provider is simply delivering calls - they have no visibility into your extensions, ring groups, or call flows.Think of it like this: the SIP trunk is the petrol, and the PBX is the car you own. The petrol station does not care how your car works, and your mechanic has nothing to do with where you buy fuel. You control the vehicle entirely.SIP trunks are priced in a few different ways. Some providers charge per channel (one channel = one simultaneous call), so 4 channels means 4 calls can be active at once. Others charge per minute of outbound call usage. Still others offer unlimited call plans with a fixed monthly fee per trunk. Australian SIP trunk providers typically charge anywhere from around $10 to $30 per month per channel depending on inclusions, with call rates from $0.01 to $0.05 per minute for local and national calls.

What Hosted PBX Actually Is

Hosted PBX (also called cloud PBX) means the PBX software lives in the provider's data centre, not yours. You do not install anything, you do not manage any server, and you do not configure SIP settings. The provider handles the entire system - the infrastructure, the software updates, the call routing engine, and the connection to the public phone network.You get access to a web portal or admin dashboard where you can configure call flows, set up extensions, record voicemail greetings, and manage users. But the engine running all of that sits in the cloud, managed entirely by the provider. You are effectively renting access to a phone system rather than owning one.Pricing is almost always per seat per month. A seat is a user - one person who needs a phone extension. At the small business end of the market, hosted PBX plans in Australia typically range from around $20 to $45 per seat per month, with the higher end including features like call recording, advanced reporting, and CRM integrations. The SIP trunk connection is bundled in - you do not need to think about it separately.The analogy that works: hosted PBX is hiring a car with the driver included. You get in, say where you want to go, and someone else handles everything under the bonnet. If something breaks, you call the provider. If you need a new feature, you ask the provider. You never open the engine bay.For more detail on how to choose between Australian hosted PBX providers and what to look for in each plan, our buying guide covers the main AU-based and international options operating in the market.

Side-by-Side Comparison

The Cost Crossover Point

This is the question that matters most for growing businesses: at what seat count does running your own PBX with SIP trunks become cheaper than paying per-seat hosted pricing?The short answer for the Australian market: roughly 15 to 25 seats, depending on call volume and which PBX software you use. Here is why the range exists.Hosted PBX costs scale linearly with headcount. If you pay $30 per seat and add a staff member, you pay another $30. At 10 seats that is $300/month. At 25 seats it is $750/month. The per-seat model is predictable and low-risk at small scale, but it does not benefit from any economies of scale.SIP trunks scale with call volume, not headcount. A 25-person business where staff are mostly in meetings, on email, or doing site visits might only need 6-8 simultaneous call channels. At $15-25 per channel, that is $90-$200/month for the trunks. Add 3CX licensing at roughly $200-$350/year for a 25-simultaneous-call licence, and you might be running the whole system for $150-$250/month - a fraction of the $600-$900/month you would pay per-seat.The crossover is not purely mathematical, though. You have to factor in the cost of managing the PBX - either your own IT time or fees paid to an MSP. If you are paying a managed service provider $100-$200/month to maintain your 3CX instance, that eats into the savings considerably at the 15-20 seat range. The crossover only clearly favours SIP trunks once the per-seat savings outweigh the management overhead.

Australian Businesses: NBN Considerations for Each Model

Both SIP trunks and hosted PBX run over your internet connection - but they respond differently to the connection quality realities of the NBN.

SIP Trunks and NBN

SIP trunks are more sensitive to internet connection quality than hosted PBX solutions because all QoS (Quality of Service) configuration sits at your end. Your router or firewall must be configured to prioritise SIP traffic over general internet usage, otherwise a large file download or video call can degrade voice quality in real time. On NBN, the connection types that work well for SIP trunking are FTTP (fibre to the premises), HFC, and FTTC - these offer consistent upload speeds and low jitter. Fixed wireless and satellite are problematic: variable latency makes SIP trunking unreliable for business use.SIP ALG (Application Layer Gateway) is enabled by default on many NBN modem/routers. This feature was designed to help SIP traffic traverse NAT, but it frequently corrupts SIP packets instead and causes one-way audio, dropped calls, and registration failures. Anyone setting up SIP trunks on an NBN connection should disable SIP ALG in the router settings as one of the first steps.

Hosted PBX and NBN

Hosted PBX providers typically handle more of the QoS complexity internally. Because calls are managed server-side by the provider, they can apply traffic shaping and call quality controls at the platform level. Your phones connect to the provider's infrastructure over standard HTTPS or SIP-TLS, and many providers include built-in failover to mobile if your internet connection drops.That said, hosted PBX still requires a stable internet connection with adequate upload bandwidth. A general rule is to allow 100 kbps of dedicated upload bandwidth per simultaneous call. A 5-seat office that might have 3 calls running at once needs at least 300 kbps of clean upload capacity - easily achievable on most NBN plans, but worth checking if you are on a low-tier plan or a congested FTTN connection.

When SIP Trunks Are the Right Choice

SIP trunks make sense in these specific scenarios:You already have an on-premise PBX. If you are running 3CX, FreePBX, Asterisk, or a legacy Cisco or Avaya system, SIP trunks let you replace your ISDN or PSTN lines without replacing the entire system. This is the most common SIP trunk use case in Australia - businesses migrating to the NBN or cutting ISDN costs and keeping the PBX they know.You have 20 or more seats. Once your team is large enough, the per-channel cost model of SIP trunks becomes materially cheaper than per-seat hosted pricing. If your 30-seat business has moderate call volume and needs 10 simultaneous channels, you are likely paying $150-$300/month in trunking costs versus $600-$1,200/month in per-seat fees.You have an IT team or MSP relationship. SIP trunks require someone who can configure the PBX, manage SIP credentials, troubleshoot one-way audio issues, and handle failover scenarios. If you have that capability in-house or a trusted MSP who handles it, the complexity barrier is not a barrier at all.You need maximum control over call routing and features. A self-hosted PBX with SIP trunks gives you access to every feature the PBX software supports - complex ring group logic, call centre queues, detailed call analytics, custom hold music, CRM integrations at the PBX level, and more. Hosted PBX providers limit you to the features they choose to expose in their portal.You have high outbound call volume and want to optimise call rates. Per-minute SIP trunk pricing can be cheaper for high-volume outbound calling than the flat-rate model of most hosted PBX plans, which are priced assuming moderate usage.

When Hosted PBX Is the Right Choice

Hosted PBX is the better choice in these scenarios:You have no existing phone infrastructure. Starting from zero, a hosted PBX lets you have a working multi-extension phone system in a few hours. You do not need to buy or lease a server, configure SIP trunks, or know what a codec is. You sign up, create extensions, plug in IP phones, and you are live.You have between 1 and 15 seats. At this scale, the per-seat fee is manageable and the savings from SIP trunks do not yet outweigh the complexity and management overhead of running your own PBX.You have no internal IT capability and no MSP. SIP trunk setups require someone who understands networking, SIP configuration, and firewall rules. If that person does not exist in or around your business, you are taking on a level of ongoing technical risk that a hosted PBX completely removes.You need to go live fast. A new business, a new office, or a team being stood up quickly can have a hosted PBX running same-day. Provisioning and configuring a self-hosted PBX with SIP trunks typically takes several days to several weeks, especially if number porting is involved.You want a predictable monthly bill. The all-in per-seat model is easy to budget. Your phone costs scale exactly with your team size, and there are no surprises from unexpected call volume or channel capacity.You want the provider to handle reliability. When a hosted PBX provider has an outage, the fix is their problem. When your self-hosted PBX goes down, it is yours. For a business owner who does not want to be troubleshooting a phone system failure at 8am on a Monday, that accountability difference matters.

Hybrid Models: The Best of Both

Some businesses run a hybrid approach: a hosted PBX for general staff phone extensions, plus direct SIP trunks for high-volume outbound calling from specific teams or roles.The typical scenario is a sales or outbound team sitting inside a hosted PBX environment, but with a separate SIP trunk connected directly to a softphone or auto-dialler platform to handle volume calling at lower per-minute rates. The main PBX handles inbound, extensions, ring groups, and IVR. The SIP trunks handle the high-volume outbound workload where per-minute costs matter.This approach is not common at the SMB level - it adds complexity that most small businesses do not need. It becomes worth considering once you have a team making hundreds of outbound calls per day where the per-minute savings on SIP trunk rates justify the additional setup and management.A simpler version of a hybrid is a hosted PBX provider that also offers SIP trunk add-ons - effectively letting you control channel capacity separately from seat licensing. A handful of Australian providers offer this configuration. Check with your VOIP provider whether they support a split model before building separate infrastructure.

Common Mistakes

Confusing SIP trunks with a complete phone system. A SIP trunk is not a phone system. You cannot plug phones into a SIP trunk directly. You need a PBX sitting in between. This misunderstanding leads businesses to sign up for SIP trunk accounts and then realise they have no way to use them.Choosing SIP trunks without an IT plan. Committing to a SIP trunk and self-hosted PBX without confirming who will manage the setup and ongoing configuration is a common mistake. The configuration is not trivial - firewall rules, SIP ALG settings, codec negotiation, failover routing, and software updates all need ongoing attention. Budget for the management cost before deciding this is the cheaper option.Under-provisioning channels. A business that estimates it needs 4 simultaneous call channels based on a single day of observation can easily run short during busy periods. The result is callers hearing an engaged tone rather than reaching the business. Model your peak usage, not your average usage, and add at least one spare channel as a buffer.Ignoring SIP ALG on the NBN router. This is the most common cause of call quality issues on new SIP trunk deployments in Australia. SIP ALG is enabled by default on many NBN modem/routers and frequently breaks SIP traffic. Turn it off before troubleshooting anything else.Choosing hosted PBX at large scale because it feels simpler. The simplicity of hosted PBX is real and valuable - but paying $900/month for a 25-seat hosted PBX when a managed SIP trunk setup could cost $250-$350/month is a meaningful cost penalty that compounds over years. Run the numbers before assuming the simpler option is the right one.Not planning for number porting before switching. Whether you are moving to SIP trunks or a hosted PBX, porting your existing phone numbers takes time - typically 2 to 15 business days in Australia depending on your current provider and number type. Start the porting process early and confirm your existing provider's porting process before you lock in a go-live date.

Your Next Steps

Use this checklist to determine which path suits your situation:Step 1: Count your seats. How many staff need phone extensions? Under 15: lean strongly toward hosted PBX. 15-25: model both options. 25+: SIP trunks with a managed PBX are likely cheaper.Step 2: Assess your IT capability. Do you have someone - internal or contracted - who can configure a PBX, manage SIP credentials, and troubleshoot call quality issues? If no: hosted PBX. If yes: SIP trunks become viable.Step 3: Check your existing infrastructure. Do you already have a working PBX (3CX, FreePBX, Asterisk, or similar)? If yes: SIP trunks can replace your existing lines without changing the system. If no: you need to either stand up a PBX or go with hosted.Step 4: Check your NBN connection type. FTTP, HFC, and FTTC all support voice well. FTTN can work but may have jitter issues on older copper. Fixed wireless is marginal. Satellite is not suitable for business voice.Step 5: Get quotes for both models. Contact two or three SIP trunk providers and two or three hosted PBX providers. Build a total cost of ownership comparison that includes management time, not just the monthly fee.

What is the difference between SIP trunking and hosted PBX?

SIP trunking delivers telephone calls over the internet to a PBX system that you own and manage. Hosted PBX means the PBX software runs in the provider's cloud - they manage everything, and you pay per seat per month. The key difference is who owns and operates the phone system software. With SIP trunks, you do. With hosted PBX, the provider does.

Is SIP trunking cheaper than hosted PBX?

It depends on scale. For small businesses under 15 seats, hosted PBX is usually cheaper in total cost of ownership once you factor in the time and cost of setting up and managing a self-hosted PBX. For businesses with 20 or more seats, SIP trunks connected to a self-hosted PBX often cost significantly less per month - sometimes 50-70% less - because channel-based pricing does not scale linearly with headcount the way per-seat pricing does. The crossover point in Australia is typically around 15-25 seats.

Can I switch from hosted PBX to SIP trunks later?

Yes, but it is not a simple swap. Moving from hosted PBX to SIP trunks requires you to deploy and configure a self-hosted PBX (such as 3CX or FreePBX), connect your SIP trunks to it, recreate all your extensions, ring groups, and call flows, and port your numbers across to the new provider. The technical work involved is the same whether you are building from scratch or migrating. That said, none of it is irreversible - your phone numbers can be ported, and the transition can be managed in stages.

Do I need an IT person to manage SIP trunks?

In practice, yes. SIP trunks need to be connected to a PBX, and the PBX needs to be configured with SIP credentials, codec settings, dial plans, and firewall rules. Ongoing, the PBX needs software updates, and call quality issues require network-level troubleshooting. This is not beyond a capable IT generalist, but it is not something a non-technical business owner should attempt without support. If you do not have internal IT capability, you either need to budget for an MSP or choose hosted PBX instead.

Which Australian businesses should use SIP trunks?

SIP trunks suit Australian businesses that already have an on-premise PBX and want to replace ageing PSTN or ISDN lines, businesses with 20+ seats where per-seat hosted costs are becoming expensive, businesses with IT staff or an MSP who can manage the PBX, and businesses that need maximum control over call routing and features. They are a poor fit for small businesses without IT support, businesses that need to be live quickly, or anyone who wants a phone system that just works without technical involvement.

What happens to SIP trunks if my internet goes down?

If your internet connection drops, SIP trunks stop working - inbound calls cannot reach your system and outbound calls cannot be placed. Most SIP trunk providers offer failover options: calls to your number can be automatically redirected to a mobile number or backup line if your SIP registration drops. This failover is typically configured in the SIP trunk provider's portal and is strongly recommended for any business where missed calls have a real cost. Hosted PBX providers handle this similarly, often with more automated failover built into their platform.