Although the description inside KB 971083 is fairly sparse, the update fixes an AutoUpdate bug and adds in proper Exchange 2010 inter-op fixes. Previously, if Exchange 2010 was handling the AutoComplete duties for your organization, you would receive a dreaded "Exchange Integration Error" after logging into Office Communicator. This update fixes that error.
On a good note, you can work around this issue by placing a direct block with a URL redirect to the location of the updated communicator.msp from 3.5.6907.22.
If you want to force stragglers using Office Communicator 2007 R1 to upgrade to the new R2 version, you can place the CommunicatorVolume.MSI somewhere within the Updates directory on the Front End Server and set that URL as the static "Block with URL" to the R2 install media. Since it is using the built in authentication (at worst, offsite non-domain joined clients will have to enter in their Active Directory credentials), you don't have to worry about unauthorized users downloading the client because the URL is only given after they have logged into the Office Communicator client. No client authentication - no download allowed.
If you are curious how I have my client version filter setup, here is a screenshot:
All those individual version numbers are unnecessary for Office Communicator 2007 R1. You can use a * for the last number (QFE) if you want to catch all MOC 2007 R1 versions. For the curious, I did this originally to test out the blocking functionality with all the known 2007 R1 versions. Typically, most environments have either 2.0.6362.0 or 2.0.6362.129.
I placed the CommunicatorVolume.msi inside \\ocs-pool-fe\Updates\OC\ , so the resulting URL used for the R1 clients looks like this: https://owc.contoso.com/AutoUpdate/Ext/Files/OC/CommunicatorVolume.msi
You might notice there is a specific block in there for version 3.5.6907.9. This is on purpose, because of the bug in 3.5.6907.9. Although it isn't as seamless as the automated update, it gets the job done by pointing users to: https://owc.contoso.com/AutoUpdate/Ext/Files/OC/x32/fre/1033/communicator.msp
With those rules setup, we have Office Communicator 2007 R1 clients, of various patch levels, forced to upgrade to 3.5.6907.0, with an auto update to 3.5.6907.22. We also have the broken 3.5.6907.9 clients updating to the proper 3.5.6907.22 so that future auto updates will complete successfully without this workaround. Overall, this will help greatly with our Exchange 2010 rollout.