iPhone 4 GoPhone
 

OK, I've been reading about people using their AT&T iPhone 4 as an AT&T prepaid GoPhone. So I got a GoPhone micro sim, put it in my phone and activated it online. I got a new phone number and the site says activation was successful. But for some reason, my phone says "No Service". I don't know what the problem is! Oh, I guess I should add that the phone is jailbroken.

Your phone should be jailbroken and unlocked for it to work if the phone is from somewhere other than the US.

I understand that AT&T will not allow AT&T iPhones to use GoPhone. Non-AT&T unlocked iPhones certainly do work (my unlocked Canadian iPhone 3G works fine on GoPhone).

Factory-unlocked non-jailbroken non-AT&T iPhones should work too.