AT commands to operate GSM modems

It may some AT commands below useful for you on operating GSM modems.

Enter PIN
AT+CPIN="<pin>"

Enter PUK
AT+CPIN="<puk>","<new pin>"

PIN state
AT+CPIN?

Register network
AT+CREG?
("0,1" means logged in and "0,2" means logged out)

Show network
AT+COPS?

Show signal strength
AT+CSQ?
(somewhere between 0 and 31.99)

Data call
ATD912555666

Voice call
ATD912555666;

Enter SMS center
AT+CSCA="+351912333444"

Set to text mode and send SMS
AT+CMGF=1
AT+CMGS="+351912555666"
Please call office^Z

Preferred message service
AT+CPMS?
(+CPMS: <mem1>,<used1>,<total1>,<mem2>,<used2>,<total2>,...)

Select SIM card messages
AT+CPMS="SM","SM","SM"

Select memory messages
AT+CPMS="ME","ME","ME"

Read SMS on memory number n
AT+CMGR=<n>

Delete SMS on memory number n
AT+CMGD=<n>