I'm almost certain all the old 56k modems had the ability to fax. I'm thinking back to the late 90's when 56k was my max connection and yep the few cheap ones I had during this time were all fax modems.
Basically providing you have a telephone line you set up the modem to recognise incoming faxes (calls come through normally). This of course means handing out your telephone number to be used as a fax number too.
I maybe wrong and hopefully some can put me right if I am. It has been a while, but I'm suprized this is a feature of Windows Ultimate only, as it was available in Windows 95 as an additional download.