Capisuite is a fax and voicebox solution for capi on linux. I'm using it with a Fritz!Card 2.0 on debian.
Assuming a working capi card, you only need:
# apt-get install capisuite
Then you need to customize
/etc/capisuite/ and you will have a vbox and a fax recieving machine.
For sending a fax, I installed FaxGW. It provides a samba printer where you can dump your documents to fax and a webinterface to define where the documents should be send to.
Required is samba, a mysql server, php and the commandline tools
grep. There is a german
README with installation instructions included.