A SIM card is a small card that plugs into the inner portion of your cell phone and enables the device to connect to premium services such as calling networks and wireless data. Carriers that run on GSM networks, such as AT&T, use SIM cards to identify their customers. You must activate your AT&T cell phone's SIM Card before you will be able to access all of your device's features.
Press and hold the "Power" button on your AT&T cell phone to turn off the device. Slide the battery door off the rear of the device and take out the battery. Locate the SIM card and make note of the SIM card number that starts with the digits "89." Place the battery back into the phone and slide the battery door back on.
Go to the AT&T Wireless Activations webpage.
Check off the "Pay As You Go" box underneath the "GoPhone" heading. Press the blue "Next" button at the bottom right corner of the screen. Click within the "SIM Card Number" dialog box and input the numerical SIM card number that you obtained from the phone. Press the "Continue" tab at the bottom of the screen and wait for AT&T's servers to process your request. Print out the confirmation page that indicates your SIM card is successfully activated and begin using your AT&T cell phone.
- AT&T cellular phones can still make emergency phone calls to 911 even without a SIM card inserted.
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