You want to be looking at the Voice commands for your modem. I have listings for some of the more popular brands, like Rockwell chipsets.
Try issuing AT#cls=?
If you get a response, like 0,1,2.0,8 then you have an older Rockwell command set. If you get an ERROR, then try AT+fclass=?
If you get a response like 0,1,2,8.0 then you have a newer Rockwell command set. Let me know which you are getting, and I will forward the correct manual.
The important information is the mode 8 commands. If you support mode 8, it is an older command set. If you support 8.0 it is a newer one.
Mode 0 is data, mode 1 is fax, mode 2 is a newer fax mode and mode 2.0 is the newest. Different command sets for each of the above.
pansophic