Each T-Mobile phone comes with a SIM personal identification number (PIN) that you must enter before you install a new SIM card into the phone. Although the default PIN is 1234, you can change it at any time. After you change the SIM PIN, you must remember it. If you fail to do so, the phone will block the SIM and require a PUK code to make any changes to it. To retrieve your PIN, you’ll have to enter the correct PUK code, which you can get from a T-Mobile Customer Care agent. Tips Warnings Writer Bio
