Restoring on unactivated 3G
In short, my 3G has iOS4.0 on it, but it's not been activated and I do not have the AT&T SIM card it came with (too long of a story to go into how it got to be that way). I want to downgrade it to 3.1.2, so I made a custom IPSW with PwnageTool, but when I try to restore it in DFU mode I get the iTunes 1600 error. I read that I could try to put the phone in restore mode instead, but when I do that iTunes shows the phone is connected, but says that the phone has an unauthorized SIM card or no SIM card. Can I activate it somehow without a card in it or get around the 1600 error?
Any help is appreciated.