Linphone - Video SIP phone for Desktop and Mobile

Linphone is an internet phone or Voice Over IP phone (VoIP), it helps to communicate freely with people over the internet, with voice, video, and text instant messaging. Linphone is available for Linux, Windows, MacOSX, and for mobile phones: Android, iPhone, Blackberry. It is using SIP protocol and it is compatible with any voip operator using SIP for its network.

It provides Liblinphone, a powerful SIP VoIP video SDK that anyone can use to add audio or video call capabilities to an application. It supports IPv6, Webcam, Addressbook and lot more.