public function getMessageTypes()
    {
        if ($this->messageTypes === null) {
            $this->messageTypes = array();
            $messageTypes = Mage::getConfig()->getNode(self::XML_PATH_MESSAGE_TYPES);
            if ($messageTypes) {
                foreach ($messageTypes->children() as $typeCode => $classAlias) {
                    $this->messageTypes[$typeCode] = (string)$classAlias;
                }
            }
        }

        return $this->messageTypes;
    }