How to call main conference room from branches

I’ve got 5 offices located in different cities, all connected by MPLS network. I’m trying to set up Asterisk as my phone system. Each branch has it’s own Asterisk server with trunks for local calling. I want to add 2 things: allow extensions in office A to use the directory in office B, and 2: allow extensions from all offices to access conference rooms in office A.

I’ve installed AsteriskNow and am using FreePBX.

There is an AsteriskNow sub-forum.