A SIP trunk is a service available from an Internet Telecoms Service Provider (ITSP). It lets businesses with a PBX, use Voice-over-IP (VoIP) outside their local network by using the same connection as the Internet connection.
It's basically a call or set of calls transferred across the IP network of an ITSP using VoIP technology. SIP Trunks are used with an IP-PBX and can be imagined as replacements for traditional PST or analog circuits.
SIP Trunks are gaining in popularity as the IP networking structure improves and as they represent significant cost savings.
