question for iphone?? PLEASE HELP?

[Kittylove]

okay i have a question on an iphone. i just got an iphone 2g. but i dont pay the whole price each month because i got it from a friend and i went to a store and paid 50 dollars so they could deactivate it so i wouldnt have to pay alot each month for it. anyways, i have had it for two days and this morning i made a stupid mistake. i plugged it into my computer and it said would you like two download the itunes 3.1.2 or something like that and i pressed upload and then it restarted my iphone and now i cant get on it anymore until i go back to the store and pay 50 to deactivate it again. is there anyway i can undo that or take it off my phone? PLEASE HELP!! I WILL LOVE YOU FOREVER IF YOU CAN FIGURE THIS OUT!! <3