However, today most of this changed. I tried out the new Bria iPhone edition voip app, and it was mostly brilliant: It works. It works over wifi an 3G. The voice quality is excellent. The call application looks very much like an ordinary call application. Bria can't replace the default caller application, but on the iPhone that doesn't matter very much due to the desktop-based navigation metaphor. The only gripe I have so far is that it doesn't seem to be possible to call into the phone through 3G even with the application started. I haven't discussed and debugged this with my friendly voip vendor, so it may be a configuration issue, we'll see.
The upshot of all this is, for me, that today july 6, 2010 the age of mobile voip starts. This means that after this date call routing through the mobile network is only one of several options for making practical mobile phone calls. I'll probaly elaborate on why and how this is very important news (the future growth of Google Voice and the inevitable delamination of carriers are two issues closely related to mobile voip), but not today :-)