Currently 3G is ussing a technic call W-CDMA which has far higher bandwitdh transmission compare to CDMA2000. While WiMax is using a totaly different infrastructure, think of it as WiFi with much more wider range. U can learn more about CDMA by grabbing any basic networking book.

Anyway i think one of the key feature in this iPhone is its user interface. Doesnt matter if it uses EDGE or 3G if you have a lousy interface even with superb features pack into it, you will have a hard time learning how to send a simple sms out. Just need to look at the click wheel, even my low tech sister dont need me to teach her how to use the ipod.