What is SIP Trunking?
SIP trunking connects your existing on-prem phone system to the public telephone network over the internet — and when it beats full UCaaS.
SIP trunking delivers phone service to your business over the internet using the SIP protocol — replacing physical phone lines (PRI/POTS) that feed your existing PBX. The “trunk” is the virtual connection carrying your calls to the public network.
When SIP trunking is the right call
- You have an on-prem PBX you like (or can’t yet replace) and just want cheaper, more scalable lines underneath it.
- You need precise control of telephony infrastructure for compliance or operational reasons.
- You want granular scaling — buying channels as needed rather than per-user seats.
When it isn’t
If you’re replacing the PBX anyway, full UCaaS (hosted phones + apps + features for a per-user price) usually beats managing on-prem hardware. SIP trunking is a bridge and a niche tool, not a destination, for most businesses.
Typical SIP trunk pricing runs $10–25 per concurrent call channel/month depending on volume and terms.