Many modems can be upgraded by reprogramming their flash memories with an upgrade program which you get from the Internet. By sending this "program" via the serial port to the modem, the modem will store this program in its non-volatile memory (it's still there when the power is turned off). The instructions on installing it are usually on how to do in under Windows so you'll need to figure out how to do the equivalent under Linux (unless you want to install the upgrade under Windows).
If the latest version of this HOWTO still contains this request (see New Versions of this HOWTO) please send me your experiences with installing such upgrades that will be helpful to others.
If you need to send a file (program) to your modem, how do you do it?
First, there may be a command that you need to send your modem to tell
it that what follows is a flash ROM upgrade. In one case this was
AT** Next, you need to send the file directly to the modem.
Communication programs often use zmodem or kermit to send files to the
modem (and beyond) but these put the file into packets which append
headers and you want the exact file, not a modified one. But the
kermit program has a "transmit" command that will send the file
directly (without using the kermit packets) so this is one way to send
a file directly. Another way would be to escape from the
communication program to the shell (in minicom this is ^aj) and then:
cat upgrade_file_name > /dev/ttyS2 . Then go back to the
communication program (type fg at the command line prompt in minicom)
to see what happened.