A friend of mine bought an iPhone 3G from some T-Mobile cell phone vendor. The vendor had installed a custom 4.2.1 ipsw with the iPad baseband because iPhone 3G's wasn't unlockable at the time. That was great at first, but then my friend tried to restore the iPhone through iTunes. Because of the baseband, in the middle of the restore (the bar on the iPhone was partially filled) iTunes would vomit an error and axe the whole process, essentially bricking the device. He usually takes his computer issues to me, so I managed to fix the issue by reading forums and by finding an ipsw online with iPad's baseband.
That iPhone's been working for a while now, but if this happens again, is there a way I can revert from the iPad baseband so he can restore through iTunes without my intervention?