Yealink SIP-T22 - Manual (Page 87)

Basic Call Features
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is the second call out of three calls.
If multiple calls are placed on hold on more than one line key, you can view call details
by pressing the corresponding line key, and then press the Resume soft key to retrieve
the call.
You can use DND to reject incoming calls automatically on the phone. Callers will
receive a busy message.
You can enable/disable DND for the phone system, or you can customize DND for each
or all accounts. Two DND modes:

Phone (default): DND is effective for the phone system.

Custom: DND can be configured for each or all accounts.
You can receive incoming calls from authorized numbers when DND is enabled.
To configure the DND mode via web user interface:
1. Click on Features->Forward & DND.
2. In the DND block, mark the desired radio box in the Mode field.
3. Click Confirm to accept the change.
Note DND mode is configurable via web user interface only.