Hi, all. I'm currently using an iPhone 4 with a prepaid AT&T sim. I got the phone from a woman who did not seem to know much about it. She told me I'd have to unlock it with a Gevey sim, but I didn't have to; it just worked with my prepaid card. A few days ago, I decided to take my chances and try to update the iOS from 4.3.5 to 5.1. I did and I'm still able to use my prepaid sim. My question is: Could a carrier-locked iPhone be used as a prepaid and could it be updated without locking? I'm going to activate a T Mobile sim to see if I'm really locked to AT&T, but I haven't got around to it yet. The seller told me I'd be able to use T Mobile, but I don't think ahe knew for sure. Thanks.