1)   Express Talk VoIP Softphone 2.06
Express Talk is software that works like a telephone to let you make calls from your PC. With Express Talk you can call anyone on the internet who has installed Express Talk (or any other SIP voip softphone). Calls are free.

 2)   damaka 2.0
damaka enables you to make free phone & video calls anywhere in the world. damaka uses innovative standard's based (SIP) peer-to-peer (P2P) technology to connect you with other users. It also offers free conferencing, voicemail & file transfer.