Like other cumulative updates the package contains hotfixes previously released to ensure that you’re not having to patch together several different patch packages (we’re living in 2010 remember, patch management processes have been ironed out).  The core three issues that this CU includes that go above and beyond the hotfixes previously released include:

• 978161 (http://support.microsoft.com/kb/978161/ ) Office Communicator 2007 R2 crashes when you receive an incoming instant message notification
• 978162 (http://support.microsoft.com/kb/978162/ ) A hyperlink is converted to plain text format when you input the hyperlink into an Office Communicator 2007 R2 conversation window
• 978163 (http://support.microsoft.com/kb/978163/ ) You cannot call a user by using the Actions button in Office Outlook 2007, but you can call the user through Office Communicator 2007 R2

More information about the package can be read at http://support.microsoft.com/kb/976135

or if you just want to download the package immediately for application to your system

Microsoft Office Communicator 2007 R2 Hotfix KB 976135

Upon completion of this installation your Communicator R2 application will be running at version 3.5.6907.83