Yealink SIP-T2 SERIES Administrator's Manual page 362

Administrator's Guide for SIP-T2 Series/T19(P) E2/T4 Series/CP860 IP Phones
(Optional.) Enter the DND off code in the DND Off Code field.
4)
Click Confirm to accept the change.
3.
To specify the authorized numbers when DND is enabled 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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