function tinyurl_reverse($szAddress)
{
    $szAddress = explode('.com/', $szAddress);
    $szAddress = 'http://preview.tinyurl.com/'.$szAddress[1];
    $szDocument = file_get_contents($szAddress);
    preg_match('~redirecturl" href="(.*)">~i', $szDocument, $aMatches);
    
    if(isset($aMatches[1]))
    {
        return $aMatches[1];
    }
    
    return null;
}

echo tinyurl_reverse('http://tinyurl.com/388onbs');