Install the DIGITS app on the Tablet. The tablet doesn't have a dialer etc, so you'll need the app for that. Just sign in with your T-Mobile ID email and you should be good to go.
This thread was the product of our fantastic collaborators during DIGITS Beta! As many terms have changed and bugs have been exterminated since the Beta launched, the information here may no longer be accurate. If you still have a question, please search our active threads or ask a new question in the DIGITS space!