Usually...
I believe the command is ATI# where the # is usually from 0 to 10.
Open up Hyperterminal, and create a connection directly to the modem's com port. Once connected, type in ATI, and then continue with ATI0, ATI1, and so on until it responds with ERROR.
On one of the lines you should see a string identifying the modem, most of the time if I recall, it's ATI3 that does, but not necessarily always.