A SIP trunk connects a phone system you own and run to the telephone network; a hosted PBX (cloud PBX) is a phone system the provider runs for you, sold per user. Choose a SIP trunk when you already have a PBX or contact center platform and want control over carriers and call costs; choose a hosted PBX when you want a working phone system without managing one.
What is the difference between a SIP trunk and a hosted PBX?
Both use VoIP, but they cover different layers. The PBX is the system that manages extensions, ring groups, queues, IVR menus and voicemail. The SIP trunk is the line from that PBX to the outside world. With a hosted PBX, the provider supplies both the PBX and the calling service. With a SIP trunk, you supply the PBX and the provider only carries the calls. The basics are in what is SIP trunking and SIP trunk vs VoIP.
SIP trunk vs hosted PBX: side by side
| SIP trunk + your PBX | Hosted (cloud) PBX | |
|---|---|---|
| Who runs the PBX | You or your integrator | The provider |
| Pricing | Per channel and/or per minute | Per user per month, often with call bundles |
| Cost at scale | Usually lower for many users or high call volume | Grows with every seat |
| Carrier choice | Free: several trunks, routes per destination | Usually the provider's own routes |
| Customisation | Full: dialplan, integrations, dialers | Limited to the provider's features |
| Skills needed | VoIP and network knowledge | Basic admin through a web portal |
| Maintenance and security | Your responsibility | The provider's responsibility |
Do I need a SIP trunk if I have a hosted PBX?
Usually not. A hosted PBX includes the connection to the phone network, so you only need internet access and phones or apps. Some hosted platforms let you bring your own SIP trunk ("bring your own carrier"), which is useful when you need cheaper international routes or numbers the provider cannot supply. Ask whether the platform allows it before you sign.
SIP trunk vs cloud PBX vs UCaaS
- Cloud or hosted PBX: a phone system in the cloud. Calls, extensions, queues and voicemail.
- UCaaS (Unified Communications as a Service): a cloud PBX plus video meetings, chat and collaboration in one subscription, such as Microsoft Teams Phone or Zoom Phone.
- SIP trunk: only the calling connection. It can feed an on-premise PBX, a self-hosted PBX in a data center, or a UCaaS platform that supports external carriers.
A platform that serves other businesses through APIs is a CPaaS rather than a UCaaS. CPaaS platforms buy SIP trunks and wholesale routes in volume.
Which fits your business?
| Situation | Better fit |
|---|---|
| Small office, no IT staff, standard needs | Hosted PBX |
| Existing on-premise PBX still in good shape | SIP trunk |
| Call center with a dialer (Vicidial, other platforms) | SIP trunk (see SIP trunk for call centers) |
| Heavy international calling | SIP trunk with routes per destination |
| Staff spread across many locations, mostly internal calls | Hosted PBX or UCaaS |
| Reselling voice to your own customers | Own PBX or softswitch with SIP trunks |
If you choose a SIP trunk, plan the details: number of channels and calls per second (see SIP trunk channels and CPS), DIDs for inbound calls (see DID numbers), and protection against fraud on an exposed PBX (see VoIP toll fraud).
Routes for your own PBX
If you run your own PBX or platform, the call cost depends on the routes behind your trunk. VoIPMatcher sources VoIP termination routes per destination from its carriers and manages them for you. Request a SIP trunk route with your destinations and volumes.
Frequently asked questions
Is a hosted PBX the same as a cloud PBX?
In practice yes. Both terms describe a phone system that runs in the provider's data center and is delivered over the internet, so you do not install a PBX on site. Some vendors use virtual PBX for the same idea. Features and pricing vary by provider, not by the name used.
Is a SIP trunk cheaper than a hosted PBX?
Often, for larger teams and high call volumes. A SIP trunk is priced per channel or per minute, and channels are shared among users, while a hosted PBX charges every user each month. For a small office the hosted option can be cheaper overall, because there is no PBX to buy, host and maintain.
Can I run my own PBX in the cloud with a SIP trunk?
Yes. Many companies run Asterisk, FreePBX, 3CX or a similar PBX on a virtual server in a data center and connect it to one or more SIP trunks. You keep full control and carrier choice, without hardware on site. You are still responsible for updates, backups and security.
How many SIP trunk channels do I need for my users?
Size by concurrent calls, not users. Office teams rarely have more than one in three or four people on an outside call at the same time, while outbound call centers can need one channel per agent or more. Check the peak concurrent calls in your PBX reports and add headroom.
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