Well, this is a great question.
However, it screams for more.
That is, MERLIN MAIL stopped being produced at RELEASE 3.
SO, exactly what are you working on.
With Merlin Messaging, you can have PERSONAL OPERATORS for each extension, default being the Call Answer Service operator.
You can steer Auto Attendant to any number of things, including DISCONNECT.
What are you trying to do? - What results do you want?