How to Network unlock AT&T GoPhone Samsung A157

Luckily, I had an AT&T goPhone lying around after I bought Samsung Galaxy S3, but it was locked to AT&T alone. I tried to insert my airtel sim, but it asked for Network lock pin.
After searching for a solution for a long time, I finally found the solution from
here
SGH-A157 Network unlock procedure: ZAKIR GSM

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Step 1: Remove sim card from phone and turn the phone on.

Step 2: Dial *2767*3855# This will  initiate a Full reset for Samsung A157

Step 3: Once the phone restarts, dial #*7337# This will remove sim lock and freeze

Step 4: Now insert Airtel Sim card. and restart the phone. You will get TMobile signal and will start receiving messages.


That's it! Enjoy!