For sending faxes through asterisk (once successfully set up) is very easy. You can make it do some funky things. To test to see if it works though I wrote this quick script;

#!/bin/sh
#
# Work fax number = 01618771111
#

FAXDATE=`date +%s-%N`
cat <<EOF >/tmp/fax-$FAXDATE.call
Channel: SIP/fax/01618771111
MaxRetries: 1
WaitTime: 20
Set: LOCALSTATIONID=Company Name
Set: LOCALHEADERINFO=Department
Set: REMOTESTATIONID=0161100000
Application: txfax
Data: /var/spool/asterisk/fax/11158588-200709211145.tiff|caller
EOF

mv /tmp/fax-$FAXDATE.call /var/spool/asterisk/outgoing/