To get the list of avaialble operators
AT+COPS=?
+COPS: (2,”AT&T”,”AT&T”,”310410″),(0,1,4),(0,1,2)
OK

To manually select the network using the AT+COPS command,
AT+COPS=1,0,”AT&T”
OK

Check the current network
AT+COPS?
+COPS: 0,0,”AT&T”
OK