Unfortunately, the standard license overview of Exchange 2010 does not provide much information. You cannot see what Enterprise licenses are required for, so if you have activated an Enterprise feature by mistake, you will have to search for a long time before you can deactivate it again.
However, there is a script in Technet that breaks down the licenses in more detail. This allows you to deactivate the features that require an Enterprise CAL.
I have adapted the script a little so that server licenses are also included. The adapted script can be downloaded here:
[wpdm_file id=9]
The original script can be downloaded here:
http://gallery.technet.microsoft.com/68321b75-ab3d-4e04-9fe1-6a42de23b67f#content