SIP stands for Session Initiation Protocol. It’s used to set up voice connections with VoIP telephony. A SIP trunk allows you to route voice calls via an internet connection, both in- and outbound. It’s a bridge between a traditional phone line (PSTN) and VoIP. The word trunk makes it sound like it’s an actual device delivered in a box, but it’s not. It’s merely a set of common and widely used internet protocols. And it comes with a lot of advantages.