We just found something very interesting. When you install Skype on a 3.0 developer preview iPhone, you can use AT&T's connection to make and receive calls. It even works pretty well over EDGE. Skype treats AT&T's WWAN like a Wifi connection. I did a quick video and posted it below:
Update:we just made a Skype call over 3G to another 3.0 iPhone using 3G. The sound quality was as good, if not better than normal AT&T. (Thanks Josh!!)
BTW, if you are commenting that it