Iphone stuck in recovery mode?

My iphone 3g is stuck in recovery mode (I dropped it today). I have tried the hold and power button reset but that doesn't work. I don't know what firmware or baseband was on it because I bought it second hand and already unlocked and jailbroken with cydia. The problem is itunes is trying to update the software. I'm afraid that if update the software I will not be able to unlock the phone again. It was originally on at&t. I dont care about having it jailbroken, but I do need the sim unlock. Does anyone know what I could do?