Office Communications Server 2007 R2 offers many features that allow administrators and business leaders to consider replacing separate PBX (private branch exchange) systems with Office Communications Server 2007 R2. Features such as Response Group Service to support call routing, team call to provide call pickup group functionality, delegation scenarios to enable administrators to answer their boss’s phone, and Office Communicator Attendant Console for attendant console environments can replace many, if not all, of the traditional PBX services. This deployment walkthrough describes a fictitious company, Litware, that uses the deployment of Office Communications Server 2007 R2 to move most of its users on its US site to Office Communications Server 2007 R2 and to replace the entire PBX on its German site. This document focuses on Office Communications Server 2007 R2 Enterprise Voice and its configuration. Because the dial plan is the heart of any voice system, configuring the dial plan in Office Communications Server 2007 R2 comprises a major portion in this walkthrough. Furthermore, as part of this migration, Microsoft Exchange 2007 Unified Messaging (UM) will replace existing voice mail functionality for Office Communications Server 2007 R2 users. Configuration of Microsoft Exchange 2007 Unified Messaging for use with Office Communications Server 2007 R2 will be described in depth.