How to Deactivate a SIM Card on T-Mobile
A lost or stolen cell phone is not only an inconvenience, but it can cost money if someone else runs up your wireless bill. If you use T-Mobile as your wireless carrier, prevent extra charges by deactivating the T-Mobile SIM card in your phone. The SIM card contains your T-Mobile wireless subscriber information, which enables you to make and receive calls on the T-Mobile network. The SIM card can be deactivated remotely.
Call the T-Mobile customer service number at 800-866-2453
Follow the instructions from the automated phone system to speak to a live representative.
Tell the representative that you want to deactivate your SIM card, then give the rep your T-Mobile account number, password and phone number when he requests them. You can find your account number on your wireless bill. The rep deactivates the SIM card automatically over the air.
Ask the representative to send you a new SIM card and/or phone so that you can resume service.