If your organization leverages Public Internet Connectivity (aka: "PIC") in conjunction with their Live Communication Server 2005 and/or Office Communications Server 2007 servers, you may not be able to successfully communicate with (or see the presence status of) America Online Instant Messenger users.
look at Scott's blog: http://blogs.msdn.com/scottos/archive/2008/12/02/office-communicator-clients-cannot-communicate-with-contacts-homed-on-aol.aspx
