2. Set up your new device.
Current T-Mobile customers upgrading to a new device: Use the new SIM card that came in the box with your device. If you bought an iPhone, the SIM may already be installed. See how to install and activate your SIM at t-mobile.com/SIM.
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New customers or new phone lines: When your T-Mobile SIM Starter Kit arrives, follow the set-up instructions to insert the new SIM into your device and activate. Or see how at t-mobile.com/SIM.