I have an apple watch ultra with T-Mobile and I'm getting att phone service. what issues could i have if i keep watch on T-Mobile services

The simplest answer is you cannot have cellular service on the watch, which is different from the cellular service on your iPhone. That's just not possible. Your iPhone and Apple Watch must be on the same carrier. As your mom's watch is through T-Mobile on installment, you'll need to find out from T-Mobile what would be required to move the watch to a different carrier and there are sure to be costs associated with such a move.

No one here can help you with this. This is between you and T-Mobile.

So I actually have an Apple Watch ultra and iPad 10th Gen on Att. I have my iPhone 13 plus on spectrums service (Verizon), with this though I cannot use my cellular on my watch until I move my phone over. With this though, the Watch still syncs to my phone so it’s basically just the regular GPS version.

hope this helps!

You're mother's going to need to find out the terms of the installment contract she signed with TMobile. It may be that if you remove the number from TMobile by porting it to AT&T, your mother will have to pay off the contract. But, no, I don't believe you'll be able to use the watch through TMobile if your number is ported to AT&T as the watch shares a SIM with the phone.

Yes u can u gotta to set same Apple ID but different family member . I T-Mobile wat with Verizon iPhone. So you’re wrong

I beg to differ, I recently got the Apple Watch ultra through AT&T on installment payments because my girlfriend didn’t like the watch. She gave it to me, and I have T-Mobile. I connected it without any issues and added cellular data to it

How did you do that