Linux Step By Steps
PCI MODEMS GENERAL INSTALL

From: Rich McClain Jr <rich@oakview.homeip.net>

1. mknod /dev/ttyS4 c 4 68
2.IF you have a kernel which is less than 2.2.x :
mknod /dev/cua4 c 5 68
3. ln -s /dev/ttyS4 /dev/modem
4. chmod 666 /dev/ttySx (where x is the com port)
5. chmod 666 /dev/modem
6. cat /proc/pci

write down the following information: first I/O range and IRQ.

as in
----
Bus 0, device 17, function0:
Communication controller: Unknown vendor Unknown device
(rev 0).
Vendor id=11cl. Device id=480
Medium devsel. Fast back-to-back capable. IRQ 11.
Master Capable
No Bursts
Min Gnt=252.Max Lat=14
Non-prefetchable 32 bit memory at 0xe4000000.
I/O at 0x6400.
I/O at 0x6800.
I/O at 0x6c00. }

7. Write down the first I/O range and IRQ. The IRQ and I/O range will be different depending on your computer.

setserial /dev/modem uart 16550A port 0x6400 irq 11

8. Try out these settings in a program like minicom (I didn't do this part because I don't know how to use minicom and I am admittedly a lazy person)

9. goto /etc/rc.d/ directory and enter in as last line setserial /dev/modem uart 16550A port 0x6400 irq 11

A couple of conditions:
If your kernel is 2.2.x or greater skip step 2.
If you don't know how to use minicom and or are lazy skip step 8.

Good Luck and hope this works for you.