Your SIM card is locked with a PIN (personal identification number) so that an identification code is required to make phone calls and use mobile data. This way, no other person can misuse your SIM card to make phone calls or use the mobile data connection.

You can change this PIN given by your network provider.

Android 10/11/12
1. Open the settings
2. ,,Security"3. ,,SIM card lock"
4. ,,Change SIM PIN"

5. Enter old SIM PIN 1x and confirm with "OK"  6. Enter new SIM PIN 2x and confirm with "OK"