Hello Benoit, thank you for adding this information. The problem is indeed that one: udev is not triggering any event when the IAX modem device is created. This lead to a not existing dev-%i.device and hence, to a non activation of the faxgetty by systemd.
The solution is to start the device manually. In your case, if the IAX modem are started at boot, you may just leave the changes you have done to the unit, and enable it for starting at boot time. I am looking for a different approach that could starts faxgetty when an IAX device is created, and stops it when it is removed. I do not have a solution yet. Bye, Giuseppe
