I'm not too familiar with the Microsft Exchange end or the terminology, but I am able to access my company's global address list through the Contact application.
-When you open up Contacts, click on 'Groups' in the upper left hand corner
-Click on the account under 'Directories', usually the name of your Exchange account
-It should bring up a 'Search Directory' function.
At this screen I am able to access any of our 5,000+ employees included in the Global Address List.