I have a similar thing for my setup:
* Analog Cam in door connected through video capture board to Motion in LMCE.
* Motion detector setup through GC100 as "Doorbell" (gives me advanced warning that someone is approaching the door)
* Analog phone connected through ATA with ext 994 (wiki says to use 994...whats 996 for?)
In my setup, when someone approaches the door, my media is paused on the MD's and it goes to the camera screen for the door cam. I use the "Goto Screen" command for an orbiter, PK_Screen is 15 (don't know if thats the same for everyone, I just watched the log when I open a camera on an orbiter to see what the command should be) and the PK_Device is set to the camera device ID. I also set it to interrupt and turn on the associated devices (eg tv). I also call the "Go Back" command after 60 seconds so that my orbiters don't sit there showing the camera all day.
At the same time, a call is initiated to one of my phone extensions I didn't want it going to the mobile orbiter. I use the "Make Call" command in the telecom plug-in to make the call from my home office phone(Gigaset IP Phone) to the doorphone on ext 994. This serves two purposes...firstly the ringing phone is my audible doorbell and I can tell it's the door because of the caller ID on the phone, secondly I can answer it if I want to talk to the person.
The tricky part was getting the door phone to answer since the person at the door isn't actually pressing anything. For this, I used a relay on the GC100 as the on/off-hook switch on the analog phone and I have an event set up so that any incoming call to the door phone is automatically answered by switching the relay and automatically hangs up with another end call event.
So when someone walks up to my door, the phone rings and I can either check the camera by pulling up my nearest orbiter, or I can wander into the living room where the TV will have been turned on with the orbiter showing the front door camera. Or if I'm watching tv at the time, my media will be paused and the camera will come up.
Then after all that when I see it is someone with a clip-board wanting me to change electricity/phone/gas provider...I can ignore them.