This is an update to a previous article about adding faxing capability to a FreePBX Asterisk system.
From a NerdVittles article they point to a script available from the PbxInaFlash site.
Here is the summary:

Go to the default source download folder and download the script
cd /usr/src
wget http://pbxinaflash.net/source/fax/fax.pbx

Make the script executable and run it.
chmod +x fax.pbx
./fax.pbx

That is it. Almost too easy!