VoIP stands for "Voice over Internet Protocol" , a protocol optimized for the transmission of voice through the Internet or other packet switched networks.
More importantly (and without the jargon) VoIP refers to a standard for voice transmissions travelling over IP networks (e.g. DSL or Broadband connections). This standard holds the key to cheaper communications: Telephone over the Internet.
VoIP is often used abstractly to refer to the actual transmission of voice (rather than the protocol implementing it).
VoIP is also known as IP Telephony, Internet telephony, Broadband telephony, Broadband Phone and Voice over Broadband.
Who can use VoIP?
VoIP Telephone Services are available to anyone who has a Broadband Internet Access (DSL, Cable or better).