Lucent Technologies PARTNER Advanced Communications System Programming And Use Instructions page 345

If VMS Cover is already turned on, press the Do Not Disturb button.
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All covered calls are sent immediately to the voice messaging system until
you turn off Do Not Disturb.
To send covered calls immediately to coverage when Call Coverage and VMS
Cover are both on, press Do Not Disturb.
All calls go to the covering extension. If there is no answer, the calls go to your
voice mailbox.
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Feature Reference