Auto-answer (intercom) for extension-to-extension calls with FreePBX and Digium phones

You have a VoIP phone system running the FreePBX distribution of Asterisk with Digium phones connected to it.  Your client says "I want interoffice phone calls to be intercom style - no ringing".  Here's how to accomplish that.

First, enable it on a per-extension basis in FreePBX.

Second, install Webmin and edit the FreePBX database to change the intercom signal from "Ring-Answer" to "Intercom" (to eliminate a preliminary ring and only have a "beep" sound).