I'm writing software and I need to know what command to issue so my software can determine the model of modem.

Here are the responses to the command AT+CGMM:

Here is the response for -F1 products:

AT+CGMM<CR>

MULTIBAND 900E 1800

OK



Here is the response for -F2 products:

AT+CGMM<CR>
MULTIBAND G850 1900

OK