I am having this same problem. I've installed avantfax on 12.04 and it seemed to be working but received faxes wouldn't show up in the inbox. I had to execute this command to get previously received faxes into the inbox.
That command worked and I was able to view the faxes. Newly received faxes would still not show up in the inbox so I changed the permissions as suggested earlier in this thread with
cd /var/spool/hylafax; for i in `ls recvq/*`; do bin/faxrcvd.php $i ttyS0; done
The file owner is uucp since apache.uucp does not exist. Now I can't view any of the received faxes. The previously received faxes are still listed in the inbox but there is a red line through the preview popup and when I try to view them there are just blank pages. If I try to open the pdf it says that the pdf file does not exist but it does exist at the indicated path. Has anyone gotten this working?
chmod -R 0770 /var/www/avantfax/tmp /var/www/avantfax/faxes
chown -R apache.uucp /var/www/avantfax/tmp /var/www/avantfax/faxes