Specific numbers can be added to the user's Do Not Disturb Exception List. Calls from those numbers override DND. N and X wildcards can be used at the end of exception numbers to match a range of numbers. For external numbers, this uses the incoming caller line ID (ICLID) received with the call.
Enabling DND overrides any Follow Me or forwarding set for the user, except for calls in the user's Do Not Disturb Exception List.
When enabled, the phone can still be used to make calls. An N is displayed on DS phones and normal dial tone is replaced by system locale specific alternate dial tone unless secondary dial tone is triggered.