If you have a PIN code enabled SIM card and want to remove /disable PIN code using AT commands follow these commands,
suppose 9546 is the current PIN code , Replace 9546 with your PIN code, >>> shows the response from modem.
>>> +CPIN: SIM PIN // pin codes need to be entered
AT+CLCK="SC",0,"9546" // disable pin code
>>> +CPIN: READY