Messaging module
When selecting a recipient of a messaging module message, you can conveniently switch to the Friends tab and select one of your friends just by clicking her user name.
Fields visibility
Users can set the visibility of some fields on their public profile to Display to friends, which makes the field visible only to their friends. For more information on this topic, please refer to the Custom fields visibility chapter.
Page url: http://devnet.kentico.com/docs/devguide/index.html?friends_example_of_use.htm