IP, VoIP, SIP and other strange words which help us to make phone calls cheaper
VoIP glossary - Internet Phone
IP Phone (also known as Internet Protocol Telephone or telephony)
An IP Phone uses the internet to transmit the data comprising voice, chat and fax information the dedicated circuit-switched connections of a so-called "public-switched" telephone network (PSTN).
This means the data travels on shared lines which means you don't pay PSTN tolls associated with regular telephone service providers.
® Callsend.com - 2006