Just create a COM port for the modem for issue the command by hyperterminal
At+FCLASS=?<CR>
if you see that the response have a option 1 or 2 , like
+FCLASS: (0-2)
or
+FCLASS: (0-1)
it is able to send fax, but if the response is ERROR or something like
+FCLASS: (0)
Or it is more easy to test with command
AT+FCLASS=1<CR>
or
AT+FCLASS=2<CR>
To see will it return OK..
Notice that for GSM Fax, you have to apply the service from the operator and it is quite expensive in Hong Kong (~$3 HKD per minute)
it should be not possible to send fax