AVOXI - AVOXI to deliver amazing call quality & an exceptional customer service experience.
Linphone - Linphone is an internet phone or Voice Over IP phone (VoIP).
Global Call Forwarding - Global Call Forwarding offers local and international toll free numbers which can be forwarded to any phone, anywhere in the world.
Zoiper - Cross-platform VoIP softphone dialer for SIP and IAX systems
Ameyo - Ameyo is a powerful and highly flexible IP-based contact center software that lets you have a personalized interaction with every customer across multiple channels, thereby driving customer engagement to a level par excellence.
Sipdroid - Free and open-source SIP/VoIP Client