AT&T have a fee-free 30-day cancellation policy [1]. AT&T will refund any activation fees, but you're still liable for any usage fees.

If you cancel after the 30 days, there is an early termination fee of $325.00 (minus $10.00 for each completed month).

[1] http://www.wireless.att.com/cell-phone-service/specials/iPho...

There shouldn't be. I believe most cell companies give you a 30 day window to change your mind and cancel service.

Verizon does, and I ended up taking advantage of that when I returned the Droid and switched back to the iPhone after 2 weeks. Unfortunately, because Verizon's billing department is terrible, they charged me the ETF even though they shouldn't have and I had to go talk to a CSR to get it removed.

To my knowledge, all carriers in the US have at least a 14 day 100% money back refund with no egregious loss. (Maybe lose the $30 setup fee.)