Lync Server 2010 can be used in a Resource Forest configuration, similar to Exchange 2010. There is plenty of information on TechNet regarding the configuration for Exchange and Lync in a Resource Forest scenario.
Exchange 2010 Resource Forest Deployment
Lync 2010 Resource Forest Deployment
I won’t get into those details here as I think they are well covered. However, I would like to delve into the differences between enabling cross-forest users for Lync versus Exchange. In Exchange the process for enabling users for Linked...