You'll need to collect a bit more information..
At a root console try:
$lspci -v | less
then scroll to the part that lists your modem and
copy or writ it down...mine looks like this:
02:01.0 Communication controller: Conexant HSF 56k Data/Fax/Voice/Spkp Modem (rev 01)
Subsystem: GVC Corporation Unknown device 0219
Flags: bus master, medium devsel, latency 64, IRQ 11
Memory at ff9f0000 (32-bit, non-prefetchable) [size=64K]
I/O ports at dc00 [size=8]
Capabilities:  Power Management version 2
This shows that I have a Conexant HSF modem on my motherboard
In order to use this I had to download a software driver from Conexant
and install the driver before the modem would work...
If you have a hardware modem on a pci card or a serial port
then setserial should be able to link to the card and get you
I hope this helps.