Peers (aka SIP related experiments) is a java sip softphone.

It's open source and gives the ability to register a sip account, place and receive calls on a standard computer. It requires sun java runtime environment version 6 (or later) or openjdk. Its graphical interface has been developed using swing. It has no external dependency and its implementation is quite straight-forward. For sound management, javasound has been used. No native library has been used or developed in Peers. Peers is pure java only, thus Peers is cross-platform.

Try it now! http://peers.sourceforge.net/