According to USB terminology it's neither -- it's a "controllerles" or "Winmodem".
Click on their:
Modems 101
Controller-based or controllerless? Find out which is right for you with our interactive lesson.
box/link on the right to see what they mean.
I think this will work:
http://www.usr.com/solutions/modem101.asp
Click through to the 9th screen to see a product chart.