PhonerLite enables your PC to use it for internet telephony (VoIP , Voice over IP, SIP). You need an internet connection and an account from a provider supporting the...
PhonerLite is a free SIP softphone for Windows
sip softphone sip-client internettelephony
Jitsi (previously SIP Communicator) is an audio/video and chat communicator with full end-to-end encryption that supports protocols such as SIP, XMPP/Jabber, ICQ/AIM, Windows Live, Yahoo!, GTalk/Hangouts extensions, as well as OTR, ZRTP...
Free Open Source Mac OS X Windows Linux Android BSD Web