For those of you who have upgraded to iOS 4, you will need to actually downgrade it back to 3.1.2 or 3.1.3 to jailbreak/unlock your iPhone 2G, 3G, or 3Gs.
I was actually trying to do this for one of my friends lately but it seems like Apple has blocked people from doing this anymore BUT if you already jailbroke your iPhone 2G/3G/3Gs before upgrading to iOS4, you can still jailbreak it.
Apple uses a signature server which can be hacked via using Cydia’s signature server. The catch is that you need to actually sign your iPhone befo