Linphone- An Open source SIP phone for desktop & mobile

Linphone is an open source VOIP software capable of making voice, video and IM using the SIP protocol. This gives users easy access to a host of SIP VOIP operators across the world. You can also use Linphone’s free SIP voice/video.

Linpone on Android

It’s cross platform, available for Windows, Linux, Android, iPhone and Blackberry. Among its features are

• Support for simultaneous multiple calls with call management features like hold with music, transfer etc
• Efficient bandwidth management
• Support for plugins
• Support for any webcam with a V4L or V4L2 driver under linux and Directshow driver on windows
• Video with codecs: H263, H263-1998, MPEG4, theora and H264 (thanks to a plugin based on x264), with resolutions from QCIF(176×144) to SVGA(800×600) among others

Linphone is available in the App Store on iPhone, Android Market, and Blackberry. It is also available in the Ubuntu repos and as a .exe file for Windows.