I just got this giong, works a treat. I was getting exactly the same symptoms as the others listed here - the phone would briefly flash with "Dialing" and then stop. Fixing this was simply a matter of asking my service provider (Orange UK) to enable Fax services on my SIM - you do need to ask for it seperately, even though my phone was already set up and working fine with GPRS.
Another question here was how to send faxes from the command line. The panther fax service is simply a GUI interface to the following commands.
To make the fax:
fax make filename
this creates a TIFF image of the file, which can be in PDF, text etc. - the files creates are <filename>.001 etc. Then:
efax -d/dev/cu.Bluetooth-Modem -x/var/spool/lock/LCK..cu.Bluetooth-Modem -vewincf -iZ -i 'E0&D2S7=120&C0M1X4' -oh -l 'yourfaxnonumber' -t destfaxnumber filename>'
destfaxnumber is in the form of an AT command, so you need a T prefix and no plusses etc., eg
Hope that helps. Don't know if I'll ever use it but from a gadget point of view it's great fun.