I use the message notification myself. What I had done was I contacted my cellular carrier and had them disable voicemail for my cellular phone. Since the only calls I get on it are forwarded from my office phone, this works fine for me, but by doing that if he is in the office, he can have his cell turned off, therefore blocking the message notification and since there is no voicemail on the cell phone, you won't have to worry about your phone system leaving a message saying "You have new Voicemail. Please enter your password." This way, if he is at his desk, phone rings, he can answer or let it go to voicemail, but when he is out of the office, just simply turn the cell phone on, put the phone on DND so that it doesn't ring (mainly to save time for the caller) and then walk away from his desk. It works really well for me. I also have pager notificaiton setup for my extension so both my cell and pager usually go off at the same time. I am using a 256 X-Class FSII at my location though, so I am not sure exactly what is available with the C-Class. Hope this helps somewhat.
