Distinctive Ring for Internal vs External Calls

Hello. I am trying to make it easier for the users of this new phone system to determine whether a call is an internal caller or external caller.

I am using FreePBX with Asterisk 11.I am using Digium D40 phones provisioned with the DPMA module.

I have seen in other forums hwo to do this, but the info is very generic. They say to modify the “Alert Info” section on inbound routes. What should I modify it to? Is there some documentation somewhere that I can reference?