Actually the hardware button isn't a good idea by your estimation quoted. Ideally, the mobile device should adapt to the context (meeting in the calendar, located at a place deemed 'work,' around others devices belonging to persons noted as 'manager' or 'executive' in your address book, etc.).

The fact that context was not taken into consideration with this mobile computer in terms of utilizing this aspect of its communication from the default setup is probably more damming than missing a button - to which you are asking a person to modify their behavior to the device and context instead of the created modifying itself to the creator/user