well i have at&t, im about to buy an iphone. i know it'll have 1.1.2 with the newer 4.6base but im wondering if i downgrade it, jailbreak it, re-upgrade it, i know it can't be unlocked but i can i pop my at&t sim back in without problems? i jus want 3rd party apps and stuff.

sorry its a newb question, i searched with so many threads popping up i didnt know how to define my search for this specific questin. thanks