The Yealink T20 handset doesn't have a button for DND like most phones. To enable or disable DND you have to go through the menu options.
- Press the Menu button
- Select option 1 (Call Control)
- Select option 4 (Do Not Disturb)
- Use the Left & Right arrows to toggle between Enabled/Disabled
- Then press OK to save
- The DND will be highlighted at the top of the LED display when enabled
- DND = Do Not Disturb