I totally agree! Apple understands, but reality is lost on Verizon and AT&T. So apple support says same as you: cancel AW part of AT&T, port iPhone X over from AT&T to Verizon (in my case), then set up AW with Verizon.
[doublepost=1513015079][/doublepost]Summing up for Success: Thank you, Apple support, BTW!
Before you can port the AW S3 LTE to accompany your iPhone on new cellular provider, you will have to go to Watch app, tap Cellular, Tap Remove whichever plan you have syncing the phone to main account of your current cell provider, and your AW is free to fly. In my case, Verizon already has the IMEI of the iPhone X with order to port, and the IMEI of the AW, and new SIM on the way.
You will then have no AW LTE connectivity, but you can use AW with the paired iPhone until new Company's SIM arrives. Then you can pop in the new SIM and, in my case at least, notify the new company rep on her cell phone to call you back on company phone/computer to bring the watch on board through NumberShare plan.
Thanks all! Was great to be banging fingers on keyboard rather than head on table while talking to cell provider reps.