You configure an additional number as a simultaneous ring number in Microsoft Office Communicator 2007 R2. When you answer an incoming call on the device that uses the simultaneous ring number, Office Communicator 2007 R2 generates a missed call notification for this call. This behavior occurs even if the call is completed.
Note The behavior does not occur if Exchange Unified Messaging is configured in Microsoft Exchange Server.
This problem occurs because Office Communicator 2007 R2 generates a missed call notification if the call is completed on a secondary device.
To fix this problem, apply the following update:
972884 Description of the update for Communicator 2007 R2: Oct 2009
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.