diff -urN squirrelmail.orig/functions/addressbook.php squirrelmail/functions/addressbook.php
--- squirrelmail.orig/functions/addressbook.php	2004-03-14 09:29:23.000000000 +0200
+++ squirrelmail/functions/addressbook.php	2004-03-21 12:38:19.000000000 +0200
@@ -97,6 +97,15 @@
 				     'table' => $addrbook_global_table));
     }
 
+    /*
+     * hook allows to include different address book backends.
+     * plugins should extract $abook and $r from arguments
+     * and use same add_backend commands as above functions.
+     */
+    $hookReturn=do_hook('abook_init', $abook, $r);
+    $abook = $hookReturn[1];
+    $r = $hookReturn[2];
+    
     if ($onlylocal) {
         return $abook;
     }
@@ -570,5 +579,12 @@
   include_once(SM_PATH . 'functions/abook_database.php');
 }
 
+/*
+ * hook allows adding different address book classes.
+ * class must follow address book class coding standards.
+ *
+ * see addressbook_backend class and functions/abook_*.php files.
+ */
+do_hook('abook_add_class');
 
 ?>