Hi, I am using an iPhone in Japan with its official carrier, Softbank. It is jailbroken and unlocked. I study in the US, so I have been using a T-Mobile Prepaid card with my iPhone for the last year or so. However, I get awful reception from T-Mobile where my school is, while my friends who have AT&T have about 4 bars. Since I used up my T-Mobile Prepaid Balance, I was thinking about switching to the AT&T prepaid plan (GoPhone) and use the sim with my iPhone. I was just wondering, is an unlocked iPhone compatible with the AT&T prepaid card? I was only wondering because I didn't want to get a sim card that I couldn't use.