I am thinking about purchasing an unlocked iPhone off of ebay. I am with AT&T but i still have the one of the old cingular sim cards. I heard that your bill goes up like $50 if you get an iPhone. I was wondering since I am not buying from AT&T and am gonna purchase an unlocked iPhone, will my bill go up any? I have unlimited texting mobile to mobile on my plan right now. Will that stay the same on an unlocked iPhone and not go up either? I also do not have internet or any media package and don't plan to get it. Also would i be able to just pop my sim card in and be ready to use the phone? any help is appreciated. thanks.