This is a hardware (controller-based) modem. Works perfectly under linux; it needs just the regular serial driver and is accessed as /dev/ttyS0 or similar. Model 5686-02 ('B') supports only v.90; model -03 is firmware-upgradeable to v.92; model -05 ('E') supports v.92 out of the box.
I have used it for both dial-out (with penggy, the AOL dialer) and dial-in (with mgetty) and it works flawlessly. Note that US Robotics doesn't include a serial cable in the box (the modem has an RS232 DB25 connector). I would have rated it a 10 but for the lack of v.92 support.