Best way to
avoid getting a WinModem: use an
external modem instead. You're guaranteed to have a hardware
UART because it's within the COM port (or
USB controller) itself, you're guaranteed to have a hardware
DSP because, well, the serial port just plain can't
do that, and you're (almost) guaranteed compatability with any
OS because most of them just use the
Hayes commandset, and all the communication between the PC and the modem is
plaintext. It's as close to a
black box as you'll be guaranteed to get with a modem (and most modems are, indeed,
black).
On an aside note, in one of the Linux notebook HOWTOs, the "modem" in the newer models of Sony VAIO is whimsically referred to as "an RJ-11 adaptor."