Yealink SIP-T48G - Manual (Page 111)

Basic Call Features
101
Incoming calls will be rejected automatically and "n New Missed Call(s)" ("n"
indicates the number of the missed calls) will appear on the touch screen.
To activate DND in custom mode for a specific account:
1. Tap .
The touch screen displays a list of accounts registered on the phone.
2. Tap the desired account.
3. Tap the On radio box of the Status field.