I have a 3g iPhone that I would like to sell on eBay/Craigslist. It is currently running iOS 4.0 with a baseband of 05.13.04. I jb & unlocked it myself a while ago using redsn0w & ultrasn0w. I would like to wipe my phone so I can sell it. How would I do this, just fire up itunes and upgrade it to 4.2.1? If I do that can I easily jailbreak and unlock it again? I've read different accounts on what I can and can't do, so could someone clarify how I should proceed?