Doddle is a free online SIP WebPhone through which you can make phone calls from within a
It works with couple of VoIP providers or you can even fill it with your own SIP settings details.
There is no desktop software to be downloaded at all. It just uses Java plugin( JVM ) which by default exists is most browsers. Asterisk (News - Alert), BT Talk, FWD, Tpad, VoipGate, VoipUser,
Vonage are already preconfigured to choose...