The first call to arrive at the OBi starts the OBi PHONE Port ringing, with CallerID, if available. If another call arrives while the OBi PHONE Port is still ringing, the second call goes basically goes nowhere. If the first call is answered, then Call Waiting, with Call Waiting CallerID, if available, should be signaled to the OBi PHONE Port. If the first caller hangs up before being answered and the second call is still ringing, the second call should go through to the OBi PHONE Port, presumably with CallerID, if available.