Linphone

linphone.jpg

Linphone is an internet phone or Voice Over IP phone (VoIP).

* With linphone you can communicate with people using voice, video, and instant messaging.
* Linphone complies to the SIP protocol, an open standard for internet telephony
* If you subscribe a VoIP to PSTN (=classic telephony) you can reach "classic" phone lines

Similar applications: 
Skype, Gizmo5