I am curious if you have the ability to turn off 3G, do you have the ability to use Edge and 3G on the same phone? Arizona is covered by the Edge network (most of the state to include my Brother's ranch in Prescott. 3G is centered around Phoenix and Tucson. It would be nice if when out of the city area you could switch 3G off and use Edge for Data. Anyone know if this is even electronically feasible on a single device?
It will automatically switch to what the network has to offer. My previous phone went from Edge to a GPRS connection in areas that didn't provide Edge, so I'm guessing it will be the same for the iPhone and 3G.
Steve-O is correct. If for some reason 3G is not available currently in the area then the phone will automatically switch to an EDGE connection. Of course, if you have 3G turned off it will use EDGE regardless, unless you're on WiFi.