Linphone, open-source voip software

What is Linphone ?

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

With linphone you can communicate freely with people over the internet, with voice, video, and text instant messaging.
Linphone makes use of the SIP protocol , an open standard for internet telephony. You can use Linphone with any SIP VoIP operator, including our free SIP audio/video service.
linphone is free-software (or open-source), you can download and redistribute it freely.
Linphone is available for desktop computers: Linux, Windows, MacOSX, and for mobile phones: Android, iPhone, Blackberry.