Communicator 2005 is not supported in Outlook 2010. While you can use both on the same computer, integration, such as online presence indicators and starting an IM session in Outlook, will not work. This will not be fixed.
Options > Contacts > Display online stats next to name will show as enabled but is greyed out. The green or red "jelly bean" icon that users see in Outlook 2003 and Outlook 2007 is not visible in Outlook 2010. If you hover over a name with your mouse, you should see the status.
Communicator 2007 R2 (and Lync, of course) supported by Outlook 2010.
More Information
Office Communicator 2005 is not supported with Outlook 2010 (TechNet Blog)
