What is "linphone"

Linphone (contraction of Linux phone) is a free voice over IP (VoIP) service and SIP client, currently developed by Belledonne Communications in France. Linphone was initially developed for Linux but now supports many additional platforms including Microsoft Windows, Mac OS X, and mobile phones running Windows Phone, iOS or Android. It supports ZRTP for end-to-end encrypted voice and video communication.

Linphone is licensed under the GNU General Public License (GPL) and supports IPv6. Linphone can also be used behind network address translator (NAT), meaning it can run behind home routers. Linphone uses GTK+ for GUI and on Linux it can be also run as a console-mode application. It is compatible with telephony by using an Internet telephony service provider (ITSP).