Hi, I am thinking of upgrading from 3.1.3 to 4.0.1. I don't have an active AT&T account but I do have a couple of old AT&T sims that I have used to activate mine and some other iPhones in the past. I have never been asked by iTunes to enter any social security or billing zip code information but recently I have been reading that I will be require to do so if I try and activate an iPhone. My question is: is this upgrade safe? Will I get stuck with any activation issues? I bought this phone off craigslist so I have no idea what the original owner's zip code etc are. Any help would be most appreciated.