Yealink SIP-T48G Administrator's Manual page 306

Administrator's Guide for SIP-T2 Series/T19(P) E2/T4 Series/CP860 IP Phones
Multiple numbers are separated by commas.
4. Click Confirm to accept the change.
To specify the return code and the reason when DND is enabled via web user interface:
1. Click on Features->General Information.
2. Select the desired value from the pull-down list of Return Code When DND.
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