Title says it all.

I've used Ekiga and it works great, although it's a little clunky.

But I have installed no less than three SIP/H323 clients on my iPhone, all of which exhibit the exact same behavior: you can call them from NetMeeting, and you can call NetMeeting with them, and both ends will ring - but as soon as you try to answer nothing happens. NetMeeting returns to the "not in a call" state, and the phone app will merely do nothing and act as if you did not press the button. Very frustrating!

Has anyone tried to do this before? Any tips and tricks or something I'm doing wrong?