iOS5 Makes US iPhone Useless - Need2 "unblock SIM" (Istanbul)

I was wondering if there was anyone out there that could help me. I am an American and I am having a problem with my (American) iPhone. It is a iPhone 4 and I bought it on eBay. Through the use of Jail Break I have been able to use it without incident, until... I downloaded the new iOS5. Now the phone has been rendered virtually useless. I have been to several Turkcell support centers and as you know you go to five Turkcells, you get five different answers to your problem, none of which were the ones I wanted to hear. Finally I went to an independent tech and he told me that when I downloaded the new iOS5, the phone went back to the original, manufacturer settings. The tech told me that the new OS has a greater bandwidth and that Jail Break could not support it so I need to contact the provider (of which I don't have one because I bought it on eBay) and get them to "unblock my SIM" and make the phone "SIM-FREE).
Can anyone help me or direct me to someone who could help me make my iPhone work here in Turkey.
Thanks,
Marty