It works like this, when your phone is ringing on an inbound call your number shows available until you answer the call. When you dial out, your number is shown as Line In Use until you hang up. While you are in a call your phone number shows as Line In Use. Finally when your phone is idle or not in a call you will show as available.
If you do not wish to be disturbed you can press the Unavailable button on the Phone3 app screen on your smart phone and you will show as Unavailable to the switchboard app.
I am open sourcing this app. If anyone wants the code, please email me.