Linphone (contraction of Linux phone) is a free voice over IPsoftphone, SIP client and service. It may be used for audio and video direct calls and calls through any VoIP softswitch or IP-PBX. Linphone also provides the possibility to exchange instant messages. It has a simple multilanguage interface based on Qt for GUI and can also be run as a console-mode application on Linux.
Both SIP service and software could be used together, but also independently: it's possible to connect Linphone service with any SIP client (software or hardware), and to use Linphone software with any SIP service.
Audio codec support: Speex (narrow band and wideband), G.711 (μ-law, A-law), GSM, Opus, and iLBC (through an optional plugin)
Video codecs
Video codec support: MPEG-4, Theora, VP8 and H.264 (with a plugin based on x264), with resolutions from QCIF (176×144) to SVGA (800×600) provided that network bandwidth and CPU power are sufficient.[18]
Gallery
One of initial version's interface of Linphone in Linux (GNOME)