softmodem have two type :
-First one software does almost all of the work.
-The other is where the software only does the "control" operations (which is everything except processing the digital waveshapes).
There are driver to deal with these softmodem :
-HSF(Host signal family) driver deal with softmodem of the first kind.
-HCF (Host Controlled Familiy) driver deal with the second kind.
-HDA (High Definition Audio)it's not driver it's an internal modem that built with sound card, and when you want to identify your modem you have to install alsa-driver with it to make it work well with sound card.
-DGC ???
for more information about modem :
tldp.org/HOWTO/Modem-HOWTO-2.html