SIP trunking is a method of delivering telephone and other unified communications services over the Internet to customers that have SIP enabled private branch exchange (IP-PBX) solutions. SIP utilizes both Voice over Internet Protocol (VoIP) and Session Initiation Protocol (SIP) and it replaces traditional telephone lines or PRIs (Primary Rate Interface).
Traditional business phone systems consist of two key components. The PBX, which provides call management and features such as Auto Attendants and voicemail, and the PRI lines which connect calls to the PSTN (Public Switched Telephone Network) where they are routed to the destination telephone. When SIP trunks are utilized, the IP enabled PBX connects to the data network instead of the PRI lines and the voice traffic travels the Internet to connect to the PSTN. This method is typically much more cost effective than PRI lines.