proxy.php

<?php

$url = sprintf('http://adserver.adtech.de/multiad/3.0/1582/0/0/-1/mode=json;plcids=%s;grp=418;misc=%s', $_GET['placements'], time());
header('Content-type: application/json');
$content = file_get_contents($url);

if (isset($_GET['callback'])) {
    echo $_GET['callback'] . '('.$content.')';
} else {
    echo $content;
}