Changes have been made in Git (master):

commit 227b42be5a480c3b92fb74ea8f794a068b5d0682
Author: horde@albasoft.com <horde@albasoft.com>
Date:   Mon Dec 3 21:29:46 2012 -0500

     Bug: 11808  Fix GAL searching.

     Signed-off-by: Michael J Rubinsky <mrubinsk@horde.org>

  .../Core/lib/Horde/Core/ActiveSync/Connector.php   |    7 ++++---
  1 files changed, 4 insertions(+), 3 deletions(-)

http://git.horde.org/horde-git/-/commit/227b42be5a480c3b92fb74ea8f794a068b5d0682

I can't access gal from an iPhone.
I get no error, but every search returns no results.

Searching the code, I've found that maybe there are some problems 
accessing to GLOBAL vars.
These changes at Horde/Core/ActiveSync/Connector.php solved the problem:

--- pear/php/Horde/Core/ActiveSync/Connector.php.ori        2012-12-03 
19:10:13.190379525 +0100
+++ pear/php/Horde/Core/ActiveSync/Connector.php        2012-12-03 
19:10:47.109137698 +0100
@@ -298,13 +298,14 @@
       */
      public function contacts_search($query)
      {
-        if (!empty($GLOBALS['conf']['gal']['addressbook'])) {
-            $fields = array($GLOBALS['conf']['gal']['addressbook'] => 
array('firstname', 'lastname', 'alias', 'name', 'email'));
+        $gal = $this->contacts_getGal();
+        if (!empty($gal)) {
+            $fields = array($gal => array('firstname', 'lastname', 
'alias', 'name', 'email'));
              $opts = array(
                  'fields' => $fields,
                  'matchBegin' => true,
                  'forceSource' => true,
-                'sources' => array($this->contacts_getGal())
+                'sources' => array($gal)
              );
              return $this->_registry->contacts->search($query, $opts);
          }