Call waiting allows Operators assigned to the Main Line or a Department to receive incoming call notifications while all Operators are already on active calls.
If the Operator is not on an active call and someone calls, the incoming call notification will appear on all available devices. Once on a call, the incoming notification will only appear on the device where the active call is taking place. So an active call on a desk phone would mean the call waiting notification would only appear on that desk phone.
Let's take a look at enabling call waiting in Dialpad.
Enable Call Waiting
From Dialpad.com, navigate to Admin Settings > Office > Main Line. If you'd like to turn on call waiting for a Department, instead navigate to Admin Settings > Departments.
Scroll to Advanced Settings, then select Call Waiting for Operators.
It will turn on call waiting for when all Operators are already on active calls.