This has been requested heavily by partners and now finally it is ready: Deploying Lync in a Multi-Forest Architecture. The most often architecture requested was Lync being deployed in a Partner private cloud while using an Exchange Server hybrid (cloud + on-premise) deployment. This 72 page document describes how to plan and deploy this Multi-forest architecture.
This document describes the configuration steps required for a multi-forest architecture in which Lync is delivered as part of a partner hosted private cloud deployment, Exchange online is delivered by Microsoft as part of Office 365, and the customer retains control of their Active Directory User forest. The multi-forest architecture enables the coordination of authentication and application interoperability between the customer’s user forest, the hosting partner’s service infrastructure and Office 365 and is ideal for those organizations that have made the strategic decision to move the complete range of communications services (Lync and Exchange) to the cloud.