Capi4hylafax
Installation
Install the capi4hylafax package.
Setup
Run faxsetup as root user to adjust hylafax to your needs. Further adjust /var/spool/hylafax/etc/config/config.faxCAPI to your needs.
c2faxaddmodem is a nice tool for configuring your ISDN card.
Start hylafax.service and c2faxrecv.service.
Be sure that your device has the right permissions 'uucp'.
Add the following line to /var/spool/hylafax/etc/config:
SendFaxCmd: /usr/bin/c2faxsend
For hints and tips see Hylafax.