I am trying to work out how to forward calls coming in on the main external number to a mobile/cell phone in case the building needs to be evacuated for example. When trying to do this the main phone does not ring but line1 lights up as ringing and the call does not get forwarded? The internal extention of the phone is 800 or 0. Ringing 0 internally the call gets forwarded, ringing 800 it doesn't. The above happens. Any ideas on how to do this?