Fair enough -- I don't claim AT&T is perfect, and far from it. My friend's Blackberry on AT&T will randomly drop calls or refuse data connections in Manhattan, even though he'd have full signal. I'd be sitting across from him in the same restaurant, and my iPhone would be fully functional.
All that says, though, is that his particular Blackberry model + revision has worse radio implementation compared to my particular iPhone model + revision for that exact situation.
As for AT&T refusing service, back when I lived in St. Louis, before they merged with BellSouth's wireless, Southwestern Bell's wireless refused wireless service to me citing their inability to find my address. Since I lived in St. Louis County but in an unincorporated area between Creve Coeur and Maryland Heights, I was not entirely surprised. We ended up going with Voicestream (now T-Mobile), and their GSM coverage was abysmal too, especially outside town. I'm sure things have changed in the 10 years since I've moved out of the area though.
It's similar in Japan, too, or was in 2003 or thereabouts. The #2 mobile carrier, KDDI's Au, had issues with servicing my grandmother's place in a medium-sized city. DoCoMo had no issues, and everyone in town used DoCoMo. Back in Tokyo, Au had completed their 3G rollout, and had far superiour 3G coverage to DoCoMo, who had coverage on paper but their towers were too far apart to penetrate far into buildings. Again, I hear things are very different now that they have ditched PDC and are releasing W-CDMA phones exclusively.