I was looking to find a SIP softphone that is portable - targeting Windows, Linux and MacOSX. One of the most important features: handy for developers playing with SIP and VoIP.
So far, I worked mainly on Linux and there the old (obsoleted?!?!) KPhone did (still does) a great job. There are other free softphones, Twinkle is one of the best, but I needed something for MacOSX.
Few weeks ago I checked QjSimple, a project led by Klaus Darilion (which is also developer and management board member of Kamailio SIP Server). It uses pjsip library and has QT interface, porting was piece of cake - just some Makefile update.
Now, version 0.6.3 is offcially available for Windows, Linux and Mac OS X.