Group Chat and Office Communicator 2007 R2 are both included with Office Communications Server 2007 R2. Because the two features share several capabilities, it is helpful to know how the two interact. The behavior of the two features depends on which one is designated as the preferred client.
For example, when Group Chat is the preferred client, Contact Lists are displayed and can be updated within Group Chat. Office Communicator also updates its Contact Lists with these updates. If Office Communicator is the preferred client, Group Chat does not display the Contacts List and because it is not available, no IM messages or sessions can be initiated through Group Chat's Contact List. However, users can double-click participants in a chat room and initiate IM sessions by using Office Communicator.
In a scenario where Group Chat is not the primary IM client, there are two differences to note. First, a Contact List which would appear in the "My Chat" panel if Group Chat were the primary IM client does not appear. Second, participants in the particular chat room that you are in still have presence information associated with them. You can still initiate an IM session with them. To do this, you double-click on the participant's name, which opens an Office Communicator chat window.