I have a Oneplus 5 and the ZTE QUARTZ
The ZTE Quartz has the Data with paired DIGITS plan setup and is showing on my account as its own phone number.
from what I have found on t-mobile's site
I am assuming that I need to wait for the SMS message like the gear S2/3 as the sim is built in. It has been over 12hrs from when the Data with paired DIGITS was setup.
Note I have bluetooth turned off to allow for testing the watch function
Texting using the watch built in app works. ( don't know if this is just using web and that is why it works)
Phone calls just disconnect with a single beep when placed.
Note to all Called tmoble and they transferred me to the DIGITS support group and within 5 mins It was working.
Same thing happened to me, but they have not got mine working yet. They got me pass the hanging up with one beep, now for some reason it will not show my original phone number it will only show the number that was assigned to it. been almost 2 days now. SMH
Manage your T-Mobile account