The Global Address List in Exchange Server contains the contact data from all mailboxes and contacts in a company. The GAL might be searched online from many devices, but offline synchronization and Caller ID resolution are not available. The address book entries can be fetched by PeopleSync to bring them to your Mac OS X Addressbook or other apps and devices. PeopleSync will retrieve phone numbers, addresses and even the profile pictures, stored in Active Directory. PeopleSync will work with Exchange Server 2010 and 2013 as well as with Office 365 Exchange Online.
The Apple Mac OS X operating system comes with several applications for Mail, Contacts and Calendar. The apps support the synchronization with several consumer and corporate email systems. With messageconcept PeopleSync and the native CardDAV support of Mac OS X a synchronization with Exchange Server GALs and other systems to the Mac is also possible. This makes contact data from these sources available in the Mail app and all other applications, relaying on the Mac OS X Addressbook.