i have an iPhone 3g that is currently jailbroken (using spirit) and unlocked (using ultrasn0w 0.93). I am really interested in upgrading to iOS4, but i cant find a definite "yes" or "no" on whether to do it. I dont want to brick the phone. I dont currently have access to an ATT sim, so if i do this, do i lose the activation? will it even work since i previously used spirit? please help!!!