You can use the BlackBerry® Client for use with Microsoft® Office Live Communications Server 2005 to chat with other Microsoft® Office Communicator users using your BlackBerry device. To use the client, you must have a Microsoft Office Communicator sign-in name. If you do not have a sign-in name, contact your administrator.
You can send and receive email messages and use other applications on your device while the client is running. When you receive a new instant message, an indicator appears at the top of the Home screen.