Unavailable - When the call is not answered on an otherwise idle phone. If the phone is in use and the call is simply ignored, then the busy destination will be used.

Busy - When the phone is busy/active call or the call is rejected by the user. Also used on an unanswered call if the phone is in use and the user chooses not to pickup the second call.

Temporary - Replaces both Unavailable & Busy until it is deleted by the user.Use this for Out-of-Office or Vacations. Delete it when you return to your regular schedule