In the terms it says to see the section in how to notify.
HOW DO WE NOTIFY EACH OTHER?
You may contact us at www.T-Mobile.com, by calling 1-800-937-8997 or 611 from your Device, or by writing to: T-Mobile Customer Relations, P.O. Box 37380, Albuquerque, NM 87176-7380. Puerto Rico customers you may contact us at www.t-mobile.com, by calling 1-800-937-8997 or 611 from your Device, or by writing to: T-Mobile Customer Relations, B7 Tabonuco Street, Suite 700, Guaynabo, Puerto Rico 00968-3349, Attn: Customer Care Manager. Electronic notices are considered delivered when sent. Mail notices are considered delivered 3 days after mailing. For multi-line accounts, we may assign a “Primary Telephone Number” to your account for the purpose of receiving notices, as well as for other purposes. If you would like to change it, contact us.
To begin arbitration or any other legal proceeding, you must serve our registered agent. Our registered agent is Corporation Service Company and can be contacted at 1-866-403-5272. For Puerto Rico customers, our registered agent is Fast Solutions, LLC and can be contacted at Citi Tower, 252 Ponce de Leon Avenue, Floor 20, San Juan, Puerto Rico, 00918, phone: 1-787-688-5881.
You should be aware that in some states, mandatory arbitration clauses are null and void. In those states you can always have your case heard in small claims court. This is normally much cheaper than your 1/2 of the arbitration fee and it's a bigger pain for T-Mobile because they have to have someone show up at your local small claims court.
The only negative on filing in small claims is that the ruling is pretty much
worthless which is why you have all these "judge" shows.