I had some problems using capi4hylafax with linux 2.6. When trying to send a fax, c2faxsend exited after 1 second without acutally sending the fax. There were some semaphore related problems causing this behavior. The patch below changes all semaphores to POSIX thread conditions and thus circumvents the problem. I don't use hylafax any longer, but as several people reported success with this patch I'll keep providing it here.
The issues addressed by this patch are fixed in the new official release. (I didn't check this.) Please try the newest AVM version before using this patch on the old version.