Yealink SIP-T21 - Manual (Page 101)

Basic Call Features
91
Group Call Pickup
To enable the group call pickup via web user interface:
1. Click on Features->Call Pickup.
2. Select Enabled from the pull-down list of Group Call Pickup.
3. Click Confirm to accept the change.
To configure the group call pickup code on a global basis via web user interface:
1. Click on Features->Call Pickup.
2. Enter the group call pickup code in the Group Call Pickup Code field.
3. Click Confirm to accept the change.