AT&T MERLIN LEGEND System Reference Manual page 209

Features
Considerations
Feature Interactions
Auto Dial
Barge-In
Callback
Camp-on
Coverage
Direct-Line Console
Display
2-160 Do Not Disturb
Do Not Disturb must be programmed onto an available button.
If a user activates Do Not Disturb while receiving a call (either ringing or
voice announced), the call continues to ring (or voice announce). The Do Not
Disturb feature is, however, activated for the next call received.
When Do Not Disturb is activated, a user's calls ring at other telephones with
shared outside line or System Access buttons or at Coverage receivers.
When a user activates Do Not Disturb, the green LED goes on next to all Auto
Dial buttons programmed with the user's extension.
If Do Not Disturb is activated, Barge-In overrides the feature and makes the
telephone ring.
Calls to a user with Do Not Disturb activated are not eligible for Callback
queuing. If the Callback originator is using Do Not Disturb, the system overrides
the feature and the telephone rings when the busy extension or trunk is
available.
A Camp-On call does not ring when Do Not Disturb is activated.
When a sender activates Do Not Disturb, calls go to individual and/or Group
Coverage receivers. Individual and/or Group Coverage calls are not sent to a
receiver with Do Not Disturb activated. If both a sender and all receivers have
Do Not Disturb activated, the call is not sent to Coverage and the caller hears a
busy tone.
If a sender in a coverage group activates Do Not Disturb and one of the
coverage group receivers calls the sender, the call rings on the sender's
telephone.
The green LED next to an Auto Dial or DSS button on a DLC goes on when a
user activates Do Not Disturb.
When an MLX telephone user with Coverage activates Do Not Disturb and calls
are sent to coverage receivers, the receiver who answers the call sees a
message showing that call was redirected because the sender activated Do Not
Disturb.
If an MLX display telephone user tries to transfer a call to another with Do Not
Disturb active, the display shows "Incomplete Transfer."