The installation of hylafax on Debian Squeeze went like a charm. I just had to plug the UM3100 modem into the usb port and follow the instructions on the official Debian wiki.
# apt-get install hylafax-server
The only tricky part was with handling fax attachments. While there are problems getting PDF attachments to work, postscript attachments worked right out of the box as it is pure text.
It seems that ‘metamail’ is required to get PDF to work but this package has since been abandoned in Debian.
Since I do not expect to be getting volumes of faxes, I decided not to waste too much time in getting PDF to work. I am happy enough with just getting PS attachments instead.
If someone else manages to get PDF fax attachments to work on Debian (post etch), please feel free to add to the comments below.