Interesting. Thanks for the detailed explanation. This sounds like a problem that might "solve itself" per se as the more GSM handsets that AT&T replaces with 3G devices would push AT&T to replace GSM-only cells with 3G cells.
In the mean time... maybe the people who use the iPhone in the areas you describe should try jailbreaking and T-Mobile. -- "At the moment of conception."
Why... EDGE on AT&T or EDGE on T-Mobile... no advantage T-Mobile's 3G runs on a unique 3G spectrum 1700/2100 (not the global 2100MHz listed on the iPhone). -- Canada = Hollywood North