AT&T has usually been pretty flexible and willing to work with me, in my experience.
(1) Giving me a new iPhone at contract price a year before my contract expiration, after the old iPhone 4 crapped the bed and CrApple refused to help in any meaningful way
(2) Reversing charges from my phone picking up voicemail in France, even though I had only turned it on briefly in order to switch it to airplane/wifi mode
(3) Reversing charges from "roaming in Mexico" when I was in Chula Vista and the phone picked up a signal from across the border
(4) Reversing charges due to SMS spam

My bill is very constant - if it varies by more than $1, I get worried and check very closely.