To activate a T-Mobile SIM card, visit a nearby store, call the T-Mobile customer service team or activate the card online. Activation is required for new SIM cards and swapped or updated old SIM Cards.
Before calling T-Mobile customer care to activate a SIM card, the phone containing the SIM card must be on. Follow the user manual to insert the card into your phone. Once the phone is on, contact the customer care team at 800-T-MOBILE, or 800-866-2453, and inform the customer support representative that you want to activate your SIM card. The rep needs to request your phone model, IMEI, SIM card number and any other details. Once he receives the requested information, the rep can activate the SIM card.
For online activation, switch on the phone containing the SIM card. To activate a swapped card, visit T-Mobile.com/SIM, or create a new account if you are a new user. Once logged in, insert your phone number in the first blank, enter the characters from the given image in the next box and click "Submit." T-Mobile then sends a four-digit PIN to your phone number; enter this PIN on the next page and click on "Submit." T-Mobile activates the SIM card on the next page.