VoIP
Alternatively referred to as IP telephone, VoIP is short for Voice over Internet Protocol and is an Internet protocol that enables users to make calls over the Internet. The first experiment VoIP call was made in 1973 even though the first software known as "Vocaltec" that enabled end users to make calls did not appear until 1995.
This enables long distant phone calls to be cheaper, although at a lower quality of audio.
Also see: Cell phone definitions, Internet definitions, IP, Network definitions, Protocol, Skype, Teamspeak, Triple-play, Ventrilo, Voice