I have multiple phones arriving from apple.com over a two day window. If I want to swap a phone ordered on one line to a different line, can I just swap out out the nano SIM from my iPhone 5 or do I need to call AT&T? This all assumes that Apple associates the number with a the phone prior to shipping like in previous years.
Yes. Beauty of sims. People often order upgrades on one line to use them on another. If you don't already ahve LTE on whatever line you plan on using it on, you will want to call AT&T, make sure it's added.