from: http://efax-gtk.sourceforge.net/
Introduction
Efax-gtk is a GUI front end for the 'efax' fax program. It can be used to send and receive faxes with a fax modem, and to view, print and manage faxes received. It also has a socket interface to provide a "virtual printer" for sending faxes from word processors and similar programs, and can automatically e-mail a received fax to a designated user, and automatically print a received fax.
I test these in lucid 528
Btw run this in terminal:
That will create a printer name for efax-gtk called FaxPrinter for a/usr/sbin/lpadmin -p FaxPrinter -E -v socket://localhost:9900
case where efax-gtk is listening on port 9900.
so you can fax from CUPS