Address Book Settings
Can Modify Address Book
Admins have the ability to restrict users from editing the Address Book. This setting can be found in Menu > Admin > User > Settings. The name of the setting is 'Can modify Address Book'.
If the checkbox is checked, then users can add and edit entries in the Address Book, the Compose window, and/or via the File Upload utility.
If the checkbox is unchecked, then users cannot make any changes to the Address Book. To be specific, they can not add entries from the Address Book, the Compose window or via the File Upload utility.