My Phone Has a SIP Dialer

Traditional phones pass conversations over the Public Services Telephone Netwok (PSTN).

Anyone who's ever used Skype knows, though, that you can also transmit calls over computer lines. Voice gets digitized, passed as packets over IP networks to someone else's computer, and then decoded into sound on the other end.  This is Voice Over IP: VOIP.

Actually, it's more than just voice, of course. Skype also does video, but folks still call it VOIP.

Skype uses proprietary protocols for this, but there are international-standard protocols, too.  The most common buzz-TLA I hear in this arena is SIP, the Session Initiation Protocol.  People talk about "SIP calls," but SIP is actually just the protocol used to set up the calls. The calls themselves exchange RTP (Realtime Transfer Protocol) packets, which move the audio and video packets back and forth once the connection's established.