Hey guys, first post, first iPhone! I just bought a phone from craigslist from a guy. It has 3.0 on it right now. I need to unlock it to use with an AT&T sim with no data. How far should I upgrade the firmware (if any?). What firmware allows the highest flexibility? I'd like to restore it at least as it still have a bunch of his stuff on it. I tried upgrading to 3.1.3, but apparently it's unsigned by apple now, I can't find any clear guide on how to do it. Also, the phone is jailbroken, but cydia quits on startup. Thanks!