Are you ordering from ATT or APPLE? If you order through ATT they will send you return label to send the old phone back to them. If you order through APPLE it's a different story.
Here's what happened with me last year:
- Got my 6s+ fine from apple.com. Notice there was no return label.
- Called ATT and was told I could take the phone into the nearest corporate store to return the phone
- Went to the ATT store. Was told I couldn't do it that I needed to send the phone back with the return label sent to me. I told them I bought it through APPLE and I didn't get a return label.
- Called ATT and requested a label from them. They told me they would send on through email I could print off and send the phone back. Waited two days for the label to come through my email. It didn't come so I called them back. Again same thing was told they would send me the label through email. I never got it. (yes I was checking the correct email associated with my ATT account and check the junk/trash folders)
- Finally decided it wasn't worth my time and paid the rest owed on the old phone and sold it to someone local for a profit.
I am going to pay the rest owed on mine and going to sell my 6s+ again this year for a profit.