Adding Apple Watch to cell plan

You actually do it from the watch. During set up it asks you to pick your provider. I suggest going to the store though, because T-Mobile will give you 3 months free.

Thanks. I’ll give their app a shot.

And another question, are there any legit ways to check online if an older iPhone is unlocked? We have a 6 just collecting dust that we’re going to add to our service. But when I tried the SIM card I got a message saying it wasn’t compatible. Makes me think the carrier, probably AT&T, didn’t unlock it a few years back.