It is very easy. Look on ebay. I recomend seller cheapunlockcodes. Price was around 13 bucks. You will need to daownload small program which will give your coded IMEI number, which you have to send to seller. Other sellers will ask you for your IMEI directly. Seller will send you back the unlock code. It usually takes 1-2 hours to complete. Good luck!
Actually, I tried to call Cingular, explained my case. Believe it or not, the operator guide me over the phone to unlock the machine just like that. I was really impressed by the level of service.