To re-activate in iTunes requires a sim card be installed in the phone. Since you're in the US, that would be an AT&T sim card. If you don't have one, you can borrow one from someone to activate your phone. If that's not possible, you'll have to go to an AT&T store & get one. They will most likely require you sign up for service...you can cancel immediately after the phone is activated. But, bottom line...you need a sim card.