The Global Address Book can’t be displayed. BUT, it still exists in the background and will resolve names. So, if you type in the recipient’s name – John – when you click Send, it will display the list of names with John – or resolve it and send if you only have one ‘John’ in the list.
You can get the global address list entries by searching through the Find Names webpage dialog by one of the global fields defined for your users globally. So that if all your users are from LA you can just type LA into the Office field, click Find and you are done. That’s how you can get the whole list of your Exchange address book.