Polycom Conference Phone "in use" Detection System

Hi! Looking for some guidance, if anyone has done anything like this before. In our office, we have Polycom (well, now Cisco) IP conference phones (e.g. Cisco Unified IP Conference Station 7937G - Retirement Notification - Cisco).

What I'm trying to build is a light that goes outside of the conference room, that lets people know whether the occupants of the room are on a call (and therefore, do not disturb!).

There's two ways that I thought of doing this:

  1. Rigging a photocell and somehow affixing it to the phone on top of one of the 3 lights that light up when the phone is in use. When the photocell registers that the light is on, it will (somehow) trigger the light outside of the room to turn on. Still trying to figure out the best way to affix the photocell to the phone

  2. There are two ports where you can plug in additional microphones (here's a link to an extender cable: http://www.cdw.com/shop/products/Polycom-microphone-cable-15-ft/1134136.aspx). I was thinking that I could take this extender cable, plug it into the Polycom, splice the other end, and use a multimeter to determine what impulses are being sent down this cable when the phone is on, and then using that to determine when to turn on the light outside of the room.

Anyone have any experience with this, or can give me guidance on the project in general?