SIP (Session Initiation Protocol) Trunking allows companies with an in-house PBX to upgrade to Internet phone service for both internal and external phone calls.

A SIP trunk attaches to an in-house PBX or an adapted traditional PBX and then translates all incoming and outbound calls into cheap Internet calls. This means that all calls in-house are free and outside of the office are cheap VoIP calls, which can save companies thousands of dollars each year.