T-Mobile offers the options of mailing in the payment with the coupon that is mailed each month, assuming that you have not signed up for the paperless statements. You also have the option of paying the bill in person at one of T-Mobile's store locations.
The easiest way to manage payments is to sign up for automatic deductions from your bank account. Even with automatic deductions, the company still supplies you with statements of what is due and also sends a text to the primary number on the account with a confirmation number and amount withdrawn on the due date. This can be set up on the website or over the phone with an operator.
Payments can also be made over the phone and on the Internet. There is no additional fee for paying over the phone, but it does take a little longer. You also have the option to pay online by logging into My T-Mobile and following the directions in the Billing tab.