Sets the user's extension into 'Do Not Disturb' mode. Callers, other than those on the user's do not disturb exception list, receive busy or are diverted to the users voicemail mailbox. Note that with a call already connected and other calls already alerting, enabling Do Not Disturb will not affect those calls already existing. For full details of see Do Not Disturb.
When on, most phones display an N on the display. This function and the Do Not Disturb On function work in parallel, ie. setting one sets the other.