I have been fielded multiple questions lately about the mysteries of the calendaring information within Office Communicator 2007. Why does my email and SIP URI need to be the same? Why does Communicator Web Access (CWA) not pull information but it can display it? Where does the information pull/push come from? What versions of Exchange server are supported?
Understanding how and where the calendering information is relatively simple - in fact, the basic concept for the user free/busy information is back-end agnostic - Outlook on the desktop is the key component. Office Communicator uses Outlook (natively 2003 sp2 and newer) to make MAPI calls to retrieve the information. This small detail means Exchange 2003, Exchange 2007, and service pack level - it really does not matter (from a free/busy perspective) - the client can and will integrate!
This integration is possible when the user's SIP URI matches the user's email address; but what happens when this is not the case? If you install Office Communicator on a home computer and sign into your corporate OCS system, can (and should) it retrieve information from your local Outlook? It can (the should is up to you) if a simple registry change is made. By default Office Communicator compares the SIP URI to the email address of the default email profile and if they do not match, it does not integrate the two. The logic is simple - if the two integrate, conversation history, contacts, and free/busy will be folded into the OC experience. If they are not the same, an integration error is presented.
To modify the registry to all integration of your free/busy and conversation history regardless of your email address run regedt32 and set the following:
Key (you may have to create this yourself): DisableEmailComparisonCheck
Make sure Communicator restarts to load the new registry information (or simply log out and back in) to force the integration. Remember - this registry change will integrate ANY Outlook email address with ANY OCS login so test and make the end result is what you are looking for.