Yealink SIP-T56A User Manual page 301

(Optional.) Enter the anonymous call rejection on code and off code respectively in the On
6.
Code and Off Code field beneath the Send Rejection Code field.
The phone will send the configured on code or off code depending on your selection when
you enable or disable anonymous call rejection feature on the phone.
Tap to accept the change or
7.
Anonymous call rejection is configurable via web user interface at the path Account->Basic.
If phone B has anonymous call feature enabled and places a call to your phone, the call will be
rejected, and the touch screen of the phone B will display the following:
to cancel.
Basic Phone Features
301