As far as i can tell, i dont want to be on AT&T unless they really get the GSM network working here in central utah... cdma 3g Plasters utah in even the emptiest of places, 3G GSM is only available is parts of salt lake county and saint george/cedar city... that's about it. I'm really guessing its going to be a long while unless att turns into a hybrid cdma gsm network.
I've been with alltel since 04, I tried ATT for a year with the iphone 3G here in utah while I was living in salt lake, kept my Alltel account active and let a buddy of mine use my alltel line while I have my iphone... well, ATT service was horried, along with their customer service, they felt no remorse for having terrible coverage... yes the 3G is fast, not reliable, and you've really got to be somewhere in salt lake/provo valley to use the dang 3G
Back home in central utah, the iphone was just a brick... made a great ipod touch in airplane mode while I had 5 cooking bars of 3g on my alltel service in the middle of the desert on our offroading trips.