The supported bands and operators can be checked and configured using the AT+SQNBANDSEL command.
AT+SQNBANDSEL? returns the complete list of bands and operator modes supported.
Example of response (truncated):
+SQNBANDSEL: 0,standard,"1,2,3,4,5,8,12,13,17,18,19,20,25,26,28,66"
Please refer to the AT Command Reference Manual for more details on this command.