I just tried an FTDI usb serial adaptor on my C3100 to use as a serial console for a disk array at work... no problem at all, dmesg proclaimedhub.c: new USB device -2, assigned address 2
usb.c: USB device 2 (vend/prod 0x403/0x6001) is not claimed by any active driver.
usb.c: registered new driver serial
usbserial.c: USB Serial support registered for Generic
usbserial.c: USB Serial Driver core v1.4
usbserial.c: USB Serial support registered for FTDI SIO
usbserial.c: USB Serial support registered for FTDI 8U232AM Compatible
usbserial.c: USB Serial support registered for FTDI FT232BM Compatible
usbserial.c: FTDI FT232BM Compatible converter detected
usbserial.c: FTDI FT232BM Compatible converter now attached to ttyUSB0 (or usb/tts/0 for devfs)
usbserial.c: USB Serial support registered for USB-UIRT Infrared Tranceiver
usbserial.c: USB Serial support registered for Home-Electronics TIRA-1 IR Transceiver
ftdi_sio.c: v1.3.5:USB FTDI Serial Converters Driver
using cacko 1.23, I installed minicom "ipkg install minicom", having previously installed ncurses (kismet command line needs that).
started up minicom with "minicom -s" (having had to add a softlink in /usr/lib/ncurses.so.4 to the .so.4.2 file), set serial port to ttyUSB0, and voila!
the only snag was that none of the installed fonts showed up like either a PC or VT100 character set, so the on-screen boxes came up as various odd blobs.