<?php

$soapURL = "http://localhost:8080/ws/services/AssetOperationService?wsdl";
$client = new SoapClient($soapURL, array('trace' => 1, 'location' => str_replace('?wsdl', '', $soapURL)));
$auth = array('username' => 'admin', 'password' => 'admin');
$identifier = array('id' => 'your-asset-id', 'type' => 'your-asset-type');
$listSubscribersParams = array('authentication' => $auth, 'identifier' => $identifier);
$reply = $client->listSubscribers($listSubscribersParams);
if ($reply->listSubscribersReturn->success == 'true') {
    echo "Subscribers:\r\n";
    $subscribers = $reply->listSubscribersReturn->subscribers->assetIdentifier;
    if (sizeof($subscribers) == 0) {
        echo "NONE\r\n";
        exit;
    } else {
        if (!is_array($subscribers)) {
            // For less than 2 elements, the returned object isn't an array
            $subscribers = array($subscribers);
        }
    }
    foreach ($subscribers as $identifier) {
        echo "[" . $identifier->type . "] site://" . $identifier->path->siteName . "/" . $identifier->path->path . "\r\n";
    }
} else {
    echo "Error occurred: " . $reply->listSubscribersReturn->message;
}