You could use an external ISDN device with a regular
RS232 connection. I
have one, and it behaives like just any other modem
with an AT-command set.
So that means that e.g. the Eicon Diva 852 ISDN T/A
could be used? I notised that Linux is not listed as a
supported OS on their site:
http://www.eicon.com/worldwide/products/ISDN/Diva852.htm,
but from what you are saying it should still work via
RS232?
If so, would I have to use CAPI (which I know nothing
about) or does HylaFax know how to talk to the box via
RS232?