I'm thinking of getting a 5S but I'm not eligible for an upgrade, so I'm thinking about using a family member's upgrade. I did this for the 4S, but it was a nightmare; I did it over the phone and it took hours to work out, had to open up the transferor's phone and all. So, I'm hesitant to do it this time. What are the details regarding this? Can I order the iPhone online (if so, is the process any different from an Apple or AT&T order)? Will I lose my unlimited plan?