When you configure a user account you can grant the user any (or all) of the following privileges:
Federation. Allows the user to communicate with users from a
Remote User Access. Allows the user to connect to the
internal network when outside the organization’s firewall. (This
connection is typically made by going through an Edge Server.)
Public IM Connectivity. Allows the user to communicate with
users from a public instant messaging (IM) network.
Enhanced Presence. Allows the user to not only report
presence information, but to control who can access this
information (as well as how much of the information they can
When you configure a user for Office Communications Server 2007 R2 some options might not be available. For example, the option that allows the user to organize meetings with anonymous users might be unavailable. If so, that is because the setting has been configured at the forest level, and cannot be changed on a per-user basis.