have a crappy signal or SLOW data? exchange your phone..
I cancelled att and returned my iphone4 3 weeks after i bought it becasue i could not get any data during the day hardly at all. nothing, nada, and my signal here at work, and home was maybe 1 MAYBE 2 bars at most. i tried restoring, called att multiple times and nothing, so i gave up...i missed it alot, so i started asking around who had an iphone 4 with NO 3g (like me) and used EDGE, i found 2 people i know in the area who had no issues, so i decided to give att a try, found a best buy with some iphone4 in stock, signed back up, and i am so happy i did. i get full bars here at work, my data is fine (for the 2 days i have owned it) and the same when at home. i am so glad that i gave att and iphone4 another chance..
now was it the phone? sim? or an account issue? who knows, but all i know is it is working..and i hope it stays that way..glad to be back..
so to anyone having the same issues..try to exchange the phone/sim