it's not a modem that I'm using the serial port to connect with; it's my ipaq. ls -l /dev/ttyS* returns nothing, and that's where the problem begins. I can
mknod ttyS0 c 4 64
and this creates the device, but the device isn't actually linked to my serial port, it's just a virtual device linked to no physical hardware.
I tried using setserial to assign a specific IRQ range to my virtual /dev/ttyS0, but as you can see lspci lists no serial bus, so I was unable to determine which values to assign