Our company just merged with another company and the goal is to have both organizations being abe to see calendar availability and book conference rooms from either side. both organaizations are on Exchange 2010, office 2013. Both organizations would eventually be merged into one, however for now it is a challenge setting up meetings without being able to check availability and conference rooms availability. There is a trust relationship between the two forests.
I was not able to check this link due to other emergencies. Hopefully go through it this afternoon and give you a status.