iPhone 3G can't restore custom ipsw
I'm trying to restore my iPhone 3G with a custom 4.2.1 ipsw because I used the iPad baseband to unlock before, and the phone worked. Recently it stopped. Now I get either error 1603 or 1600 when trying to restore the iPhone. My Mac sees it as an iPhone in Recovery Mode but won't recover. I'm using Pwnage Tool on OSX 10.6.5. Thanks in advance.