The buzz on making phone calls from iPod Touch using software based on pjsip/pjmedia is picking up steam. Engadget, Tom Keating, even Andy Abramson of VoIP Watch has picked it up.
pjmedia is now up and running (screenshot courtesy of Touchmods):
The imminent release of the software is also mentioned.
Because the developers are using pjsip and pjmedia under GPL that means the software is free and open source, and will be available to everyone! I am sure Matt Asay, recently posting about Apple and open source would be proud 🙂
pjsip blog 
I’ve been partially involved in a separate effort to develop a softphone for the iPhone and the biggest issue we had was accessing the ear speaker and microphone at the same time.
Have you guys resolved this and accomplished full duplex audio?
Jay,
The iPod Touch port of pjsip and pjmedia is done by the smart developers at touchmods.net. And there at the moment there is no iPhone support anyway.