I'm not even sure if it's possible yet, however, I figured I would ask, does anyone know how to do this? PS. I have NO prior experience to this whole jailbreaking experience. So if it is possible please explain it in a more simple way.
There is a version of pwnagetool with a custom firmware bundle to creak a custom IPSW for 3gs, but this requires you to have a mac, a 3gs with old bootrom and already be jailbroken on 4.0.1 or below, but not with spirit or jailbreak me.