In WinXP, installs easily. Sends & receives faxes with no difficulty at all, using included FaxTalk Communicator program.

In Linux, figuring out how to do it was more difficult, but probably mostly due to my own inexperience. This thread
http://www.linuxquestions.org/questions/showthread.php?s=&threadid=219795
describes the experience pretty thoroughly.

Ultimately, I was able to send and receive faxes using efax, although it's pretty cumbersome doing that from the command line. I should probably install xfax (front-end for efax) but haven't gotten around to that yet.

In summary, you have to install the acm.o module, if you don't already have it.
Then you have to create nodes as described here:
http://www.linux-usb.org/USB-guide/x332.html
(maybe you only have to create one node)
and use efax's -d option to specify the device the modem is connected to (I used -d /dev/usb/ttyACM0)

Initially, the modem had to be connected while booting up to allow kudzu to configure it, but on subsequent reboots it seems to be necessary to keep it DISconnected while booting (but tell kudzu to "do nothing" when it reports the modem as missing).