Yealink SIP-T54S Administrator's Manual page 450

Administrator's Guide for SIP-T2 Series/T19(P) E2/T4 Series/T5 Series/CP860/CP920 IP Phones
(Optional.) Enter the DND off code in the Off Code field.
4)
Click Confirm to accept the change.
3.
To specify the authorized numbers when DND is activated via web user interface:
Click on Features->General Information.
1.
Select the desired value from the pull-down list of DND Emergency.
2.
Enter the desired value in the DND Authorized Numbers field.
3.
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