Let people take multiple calls at once. With call waiting, users can place a call on hold to answer a different call. When you are on an active call, a tone alerts you to an incoming call and you can choose to answer or ignore the call.
From the customer view in https://admin.webex.com/, go to Users and select the user that you want to turn on call waiting for.
Under Services, choose Calling, and select Call Waiting.
Turn on Call Waiting.