VoIP is an acronym for Voice over Internet Protocol. VoIP is the routing of voice and/or phone conversations over the Internet or through any other IP-based network.

Companies providing VoIP service are commonly referred to as providers, and protocols which are used to carry voice signals over the IP network are commonly referred to as Voice over IP or VoIP protocols.

Also called IP Telephony, Internet telephony, Broadband telephony, Broadband Phone and Voice over Broadband.

Session Initiation Protocol (SIP) is an application-layer control protocol for creating, modifying, and terminating sessions with one or more participants. These sessions include Internet telephone calls, multimedia distribution, and multimedia conferences.

Public Switched Telephone Network (PSTN) is the network of the world's public telephone networks. Originally a network of fixed-line analog telephone systems, the PSTN is now almost entirely digital, and now includes mobile as well as fixed telephones.