I have AT&T service, with unlimited data. I last upgraded my phone in 2012 when the iPhone 5 came out. At that time, I was able to pre-order my iPhone 5, and an appointment was set for me to go to the Apple Store and pick up my new iPhone 5. It worked very well - I was in and out of the store in 15 minutes. Is that an option this time? Or do I have to pre-order through AT&T? Will I be able to keep my unlimited data plan?