I may be getting my 3GS replaced at an Apple Store tomorrow. I was thinking of doing an "erase all content and settings" prior to my visit. My problem with my phone is slow wifi. I'm going to have the genius compare my phone to one in-store. If mine is faulty I'm going to have them replace it. So if I erase all content and settings, will my phone be operational? Or will I have to reactivate it in iTunes?