By default, each new station is set to busy when the station is on the phone and will forward to the busy destination but there's another way to handle that second call.
See the below for the steps to get it set up call waiting per user
1. To set call waiting, go to User, User Setup and click on the user to modify.
2. Then scroll down and click on Service as indicated in the example below.
***NOTE: when a second call is ringing to the user, the caller will hear the customer Music On Hold (MOH), the internal user will see the caller ID and an alert tone as the call begins to ring. They can press the HOLD key put the first call on hold and answer the call
3. Click on Call Wait as the selected Service and save
4. Lastly make sure that the call forward busy for this user is not set so that the call can ring through. The call will follow the no answer forwarding destination and timer. Be sure to adjust both Internal and External forwarding.
