Logging on to the web page today, I get this message:

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In addition, we're continually enhancing My T-Mobile to better serve you.
You'll notice that there are some new enhancements online. They include:

Viewing your current activity (unbilled summary)

Updating or changing your billing address

It gets even better from here. In the coming months, you'll be able to
change your rate plan, add or delete service features, and much more!