How to crack a locked iPhone 3g?

It had 3.0 software on it (OLDDD!!) which made it impossible to add new .ipa files of new games. I hit "Restore and update" on iTunes and it updated it to 4.2 (or at least that's what iTunes said..). Now I can't do anything but use the emergency call service. How can I activate it and unlock it so that it will work with cracked ipa files? Thanks in advace.