That's fairly straight forward.
Create three tenants (I used to all ways do this with interconnect restriction).
1 for the trunks
1 for the internal extensions
1 for the fax.
Allow all tenants access to the trunks.
Disallow the fax from the internal extension.
Ralph
But the fax will still need to dial 9....
I thought the goal was to keep it from ringing internal extensions.
OK, so lets try this:
Set up a loop back trunk that rings to DISA.
Set up an ARS route that uses that trunk. Delete all digits, add a Pause and a 9 in the Digit Mod.
Create a system speed dial that points to that ARS Route.
Ring Down your fax line to that speed dial.
This way, when the fax goes off hook, it will ring down to DISA dial, the system will insert a 9 for you.
Ralph