public function isValidType($type)
    {
        return in_array($type, array(
            self::ANY,
            self::FIXED_LINE,
            self::MOBILE,
            self::PAGER,
            self::PERSONAL_NUMBER,
            self::PREMIUM_RATE,
            self::SHARED_COST,
            self::TOLL_FREE,
            self::UAN,
            self::VOIP,
            self::VOICEMAIL,
        ), true);
    }