Change which number is primary on account

For me it was this easy, 10 minute call:

1. Install the T-Mobile App, Log in
2. Create a T-Mobile ID:
   1. Choose “ACCOUNT” at the bottom of the screen
   2. If you have more than one number, only one of the numbers may have the T-Mobile ID option
   3. Click “T-Mobile ID”, wait for it to initialize
   4. Choose "Phone Numbers" and click "Next" under "LINK NEW NUMBER". Then enter the number you want to change to Primary.
      1. You will get a text confirmation when the new number is linked.
3. Once this is done, dial 611 and get a customer support rep. Explain you want to change primary account holder, provide the PIN on the account. Tell them your number is linked to the ID (they will check this anyway).
4. They will make the change for you.