The [Google domain shared contacts API][1] allows client applications to retrieve and update external contacts that are shared to all users in a Google Apps domain.
The Google domain shared contacts API allows client applications to retrieve and update external contacts that are shared to all users in a Google Apps domain. Shared contacts are visible to all users of an Apps domain and all Google services have access to the contact list. To retrieve and update Google Apps domain users contact information, use the Directory API instead.
(copied from the Google documentation under the creative commons attribution license)
