AOpen FM56 Manual page 78

Example: +GCI: 3D indicates that the modem is set for France.
Reporting Supported Range of Parameter Values
Command: +GCI=?
Response: +GCI: (<country_code>[,<country_code>[,<country_code].......]]
Example: +GCI: (20,73,B5) The modem can be set for Canada, Mexico or the United
States.