Download form from here. Get it printed. Fill it yourself, other than mobile numbers that you want to get blocked (your respective service center will do this for you). Also leave the lower part
Enter a PIN code to lock your SIM card. The default PIN code for an AT&T SIM card is "1111". Change the default PIN code for more security. After activating SIM lock, you must enter the PIN code if you move the SIM card to another device. If you forget your SIM lock PIN code, learn how to get the PIN Unlock Key (PUK) code to unlock your SIM card.
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