Several clients can find users and groups in a Contacts service.
Apple apps
The following Apple apps can use OS X Server’s Contacts service. iOS 5 and later and OS X v10.6 and later have built-in CardDAV and Contacts service support.
Contacts 5.0 or later or Address Book 5.0 or later
Mail 4.0 or later
Messages 6.0 or later or iChat 5.0 or later
Contacts app for iOS 4.0 or later
Third-party apps
Any apps that use the Contacts framework also inherit support for Contacts service.
A client must support the CardDAV protocol to use Contacts service. Any app that supports the CardDAV protocol works with Contacts service, although it might not take advantage of additions to the CardDAV protocol specific to OS X.