AT&T and other cellular providers using Global System for Mobile Communications, or GSM, technology install SIM cards in their customers' mobile phones to identify each device to the network. If you want to take your AT&T Android phone to Europe or Canada and use a world plan there, you can do so, but first you will have to unlock the phone for use outside of the AT&T network. Otherwise, the phone won't be able to accept another carrier's SIM card. If you just use your phone without subscribing to a plan on the carrier's network, you may incur much higher charges.
Instructions
1. Push the "Home" button on your Android phone to go to the home screen, then press the "Menu" button and tap "Settings." Tap "Status" and scroll down to the IMEI number. Write down this number.
2. Call AT&T customer service at 800-331-0500 and ask the customer service representative for the unlock code for your phone. The agent may ask you for the phone's IMEI number that you wrote down in the preceding step.
3. Turn your phone off.
4. Remove the battery cover from the phone, then remove the AT&T SIM card from the device. On some Android phones, accessing the SIM card may require that you remove the battery.
5. Insert a SIM card from another mobile carrier into the phone. Re-install the battery if you had to remove it and close the back cover.
6. Power on your Android phone. When prompted for the unlock code, enter it in the provided field to unlock the phone. You may need to change the APN settings on your phone for it to work properly on the new cellular network. These settings differ depending on which mobile carrier you are using and where you are in the world.
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