What is an SIP trunk? SIP trunk is short for Session Initiation Protocol trunk, which is a VoIP technology that helps an organization make and receive calls via the internet rather than traditional phone lines. More specifically, a SIP trunk expands the communication infrastructure by connecting a company's phone system to the PSTN, thus helping the agent-customer interaction in a much more efficient manner. https://www.contus.com/blog/best-sip-trunk-providers/