In Microsoft Office Communications Server 2007 R2, you make an audio call to another user who is logged into the Microsoft Office Communicator Web Access client. However, you do not hear a ring tone until the other user answers the call.
This issue occurs because the Office Communicator Web Access server uses an incorrect identity header in the 180 ringing message. Then, Office Communications Server 2007 ignores the 180 ringing message.
To fix this problem, apply the following update:
977351 Description of the cumulative update for Office Communications Server 2007 R2, Unified Communications Managed API 2.0 Core Redist 64-bit: January 2009
Note When an Office Communicator Web Access server sends a 180 ringing message to a caller, this update includes the correct identity headers. Therefore, Office Communications Server 2007 does not ignore the ringing message.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.