I am looking to address several communication issues for an upcomming production. Our company will be using the local community theatre which is very well equiped with the exception of the backstage sound sys and (in my opinion) some important communication links. -BACKGROUND- The theatre does have a wired Production Intercom sys with jacks in the booth, pit, SR, SL. Traditional for musicals there is one headset in each location. Occasionaly there is only one backstage and 2 in the booth, depending upon the production. for straight shows there are most often 2 back stage and 2 in the booth. I am stage managing this production that will be using the space. I have not yet decided if I will run the show from backstage (SR or SL) or the booth. -THE ISSUE- My primary concern is communication with the box office, especially if I were to run the show from backstage. I would like to set up a phone sys linking backstage -or- the booth (using a switch so that only one location is functional at a time) to box office. I understand how to wire the phone so that you can talk on them- but my question is with signaling. I am looking for a way to set up some sort of light in place of the ringer (such as an LED) backstage. I would like the light to trigger when ever one location is picked-up and the other is not. i.e. The stage manager picks up the phone and thereby activates the ringer in the box office until the handset is picked up. -OR- The box office picks up the handset activating a light (perhaps flashing) backstage until the handset is removed. Making sense? How do I do that with the signaling?