I currently have an iPhone 3GS running on a Version 3.1.3 and Firmware 05.12.01. It is currently JB and Unlocked but I wanna upgrade the Version (if possible) to hopefully fix the battery issue it got from upgrading to 3.1.3. I know when I originally jb/unlocked it last time, I had to use an AT&T sim card. Will I need an AT&T sim card again to re-jb/unlock? I know I'm a lil behind times and not up to speed. but spent the last year n half overseas. Would like to find an easy step by step guide asap. Thank you