SIM card stands for Subscriber Identity Module card. The SIM card is used to store personal data on a cell phone. SIM cards hold subscriber information such as phone numbers, text messages, and e-mails. The SIM card allows a user to conveniently switch between T-Mobile cell phones without having to manually transfer all the data to the new phone. SIM cards are carrier specific, which means that they can only be used for the carrier that is listed on the cell phone. You must program a blank SIM card before you can use it.
Call T-mobile's customer service toll free number. Select activation, when prompted by automated service. Wait for a representative to come on the line.
Supply the representative with the serial number on the SIM card. You may also have to give the agent your information such as the model of phone, phone number and your name.
Remove the battery from the T-Mobile phone. Insert the SIM card in the slot designated for the SIM. Replace the battery and battery cover.
Turn the phone on. Ensure the SIM card is activated correctly. Make a phone call, or have someone call the phone to test that the SIM card is working. Call customer service to troubleshoot any issues that may occur with the activation process.