On a Windows XP-based client computer, you may experience one-way audio when an LG-Nortel IP8540 phone or a Nortel Polycom CX700 phone is used in an audio/video call.
To resolve this issue, apply the following update:
967673 Description of the Communicator 2007 R2 hotfix rollup package: April 2009
After you install this update package, you no longer experience one-way audio. There are known issues with the LG-Nortel IP8540 and Polycom CX700 devices when they are used in AV calls on some Windows XP-based client computers. These known issues are scheduled to be fixed in a later update of Microsoft Office Communicator 2007 R2.
The third-party products that this article discusses are manufactured by companies that are independent of Microsoft. Microsoft makes no warranty, implied or otherwise, about the performance or reliability of these products.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.