What we have seen in the previous section applies (for a large part) also to companies that have moved Lync (and Exchange) to the cloud but still require a resource forest configuration. Microsoft has published a document, Deploying Lync in a Multi-Forest Architecture (Partner Hosted Lync with Exchange Hybrid), at http://www.microsoft.com/en-us/download/details.aspx?id=44276, which outlines how to realize different multi-forest hybrid scenarios.

The main issue in a hybrid resource forest is related to companies requiring Enterprise Voice for Lync which is not available on Office 365. In a scenario like the previously mentioned one, our resource forest will be split between two different hosting providers (on-premises and cloud). The two hosts have no trust relationship, and this makes the deployment more complex. Exchange deployment can be online or hybrid (with an on-premises component), and depending on the decision we take about our Exchange...