As a T-Mobile customer and a future BlackBerry 10 user, I am happy that T-Mobile has created a BlackBerry 10 app to control your account. The description of the app is as follows:
T-Mobile My Account is the easiest and fastest way to connect with T-Mobile on your phone. From one easy to use application, you can view and manage your T-Mobile account, quickly access Help and How-to’s for your phone, receive customized notifications, and learn more about T-Mobile services. You can also set alerts and reminders to help you optimize your phone’s battery and performance.This is a FREE service; there are no usage charges (including data) to use the application or view account usage information.
Check out the app details via BlackBerry World.