Check if a string is a valid tax number

isValidTax.php

function isValidTax($vatid)
{
    $vatid = str_replace(array(
        ' ',
        '.',
        '-',
        ',',
        ', '), '', trim($vatid));
    $prefix = substr($vatid, 0, 2);
    $number = substr($vatid, 2);

    $iso_code_2_data = array(
        'AT' => 'AT', //Austria
        'BE' => 'BE', //Belgium
        'BG' => 'BG', //Bulgaria
        'DK' => 'DK', //Denmark
        'FI' => 'FI', //Finland
        'FR' => 'FR', //France
        'FX' => 'FR', //France métropolitaine
        'DE' => 'DE', //Germany
        'GR' => 'EL', //Greece
        'IE' => 'IE', //Irland
        'IT' => 'IT', //Italy
        'LU' => 'LU', //Luxembourg
        'NL' => 'NL', //Netherlands
        'PT' => 'PT', //Portugal
        'ES' => 'ES', //Spain
        'SE' => 'SE', //Sweden
        'GB' => 'GB', //United Kingdom
        'CY' => 'CY', //Cyprus
        'EE' => 'EE', //Estonia
        'HU' => 'HU', //Hungary
        'LV' => 'LV', //Latvia
        'LT' => 'LT', //Lithuania
        'MT' => 'MT', //Malta
        'PL' => 'PL', //Poland
        'RO' => 'RO', //Romania
        'SK' => 'SK', //Slovakia
        'CZ' => 'CZ', //Czech Republic
        'SI' => 'SI' //Slovania
            );

    if (array_key_exists($prefix, $iso_code_2_data) && !empty($number)) {
        $response = file_get_contents('http://ec.europa.eu/taxation_customs/vies/viesquer.do?ms=' . $iso_code_2_data[$prefix] . '&iso=' . $iso_code_2_data[$prefix] . '&vat=' . $number);

        if ($response) {
            if (preg_match('/\bvalid VAT number\b/i', $response)) {
                return 'valid';
            }

            if (preg_match('/\binvalid VAT number\b/i', $response)) {
                return 'invalid';
            }

        } else {
            return 'unknown';
        }
    } else {
        return 'unknown';
    }
}