Interesting..the printed instructions I got with all three X’s said specifically do NOT include anything in the box except the old iPhone...no accessories, no SIM card, no packaging. Make sure the iPhone is wiped and Find My iPhone is turned off.
The instructions did say get a receipt from USPS.
You will probably get a text from them once they receive the iPhone. My advice is to keep that text!!! One year I got the “We got it” text, then 10 days later got a “We DIDN’T get it, and we’re charging you for the remaing Next balance” text. Wtf?!?
I went to the local AT&T store and showed them the ‘We got it” text. After making a few calls they credited my acccount for the full amount. Whew!!