When businesses move to VoIP, they usually choose between two architectures: a hosted PBX or SIP trunking. Both deliver internet-based calling, but they differ in who owns and manages the call-routing system. Choosing correctly affects your costs, control, and IT workload.
What a PBX does
A PBX (Private Branch Exchange) is the system that routes calls inside an organization: it handles extensions, transfers, auto-attendants, voicemail, and connecting internal users to the outside world. The question is simply where that PBX lives.
Hosted PBX: the provider runs everything
With a hosted (or cloud) PBX, the provider operates the call-routing software in their data centers. You connect IP phones or apps over the internet, and the provider handles maintenance, updates, and feature management. This is the model most small and mid-sized businesses choose.
- Best for: Organizations that want minimal IT overhead and predictable per-user pricing.
- You manage: Your phones, your network, and your user configuration through a web portal.
- The provider manages: The PBX software, servers, redundancy, and upgrades.
SIP trunking: you keep your own PBX
SIP trunking is different. Here you own and operate a PBX (often an on-premise IP PBX, sometimes a virtual one), and you buy SIP "trunks" from a provider to connect that PBX to the public phone network over the internet. A SIP trunk is essentially a virtual version of the old phone lines that used to be physical wires.
- Best for: Larger organizations that already own a capable PBX and have IT staff to run it.
- You manage: The entire PBX and its features.
- The provider manages: Only the connection to the outside phone network and the phone numbers.
Comparing the two models
| Aspect | Hosted PBX | SIP trunking |
|---|---|---|
| Who runs the PBX | The provider | You |
| Upfront cost | Low | Higher (you own the PBX) |
| Control over features | Limited to provider options | Full |
| IT skill required | Low | Higher |
| Scaling | Add users in portal | Add trunk capacity |
How to choose
Start with what you already have. If you are starting fresh or replacing aging equipment, a hosted PBX is usually the simplest path. If you have invested in an on-premise PBX with custom configurations, SIP trunking lets you retire expensive legacy phone lines while preserving that investment. Either way, both depend on a solid, well-provisioned internet connection, so network quality should factor into your decision regardless of which model you choose.
Reliability and security implications
The two models also distribute responsibility differently. With a hosted PBX, the provider is responsible for keeping the system running, applying security updates, and maintaining redundancy across data centers, so much of the operational burden shifts off your team. With SIP trunking and your own PBX, that responsibility stays with you: you must patch the PBX, secure it against attack, and plan your own redundancy and failover. Both architectures are exposed to internet-based threats such as toll fraud and denial-of-service attempts, so strong authentication, restricted calling, and monitoring matter in either case. For organizations handling sensitive or regulated information, the question of where data such as voicemails and recordings is stored, and who is responsible for protecting it, should be settled before you commit. Mapping these responsibilities up front prevents the common surprise of discovering, after an incident, that no one was clearly accountable for a critical part of the system.