$client = new SoapClient($wsdlUrl);
$saveOrCreateSubscriberRequest = new StdClass();
$saveOrCreateSubscriberRequest->mandatorId = 0;
$saveOrCreateSubscriberRequest->listsAdditive = false;
$saveOrCreateSubscriberRequest->deleteBlankFields = false;
$saveOrCreateSubscriberRequest->sendLastNewsletter = false;
$saveOrCreateSubscriberRequest->sendWelcome = false;
$saveOrCreateSubscriberRequest->filterAntiSpam = true;
$saveOrCreateSubscriberRequest->subscribers = array();

$subscriber = new StdClass();
$subscriber->subscriberEmail = "user@example.com";
$subscriber->newsletterListIds = array(1);
$subscriber->mandatorId = 0;
$subscriber->doubleOptinTemplateId = 0;
$subscriber->changeProfileTemplateId = 0;
$subscriber->subscriberFields = array();

$subscriberField = new StdClass();
$subscriberField->fieldName = utf8_encode("VORNAME");
$subscriberField->fieldValue = utf8_encode("Vorname");
$subscriberField->confirmChange = false;
array_push($subscriber->subscriberFields, $subscriberField);

$subscriberField = new StdClass();
$subscriberField->fieldName = utf8_encode("NACHNAME");
$subscriberField->fieldValue = utf8_encode("Nachname");
$subscriberField->confirmChange = false;  
array_push($subscriber->subscriberFields, $subscriberField);

array_push($saveOrCreateSubscriberRequest->subscribers, $subscriber);
try {
  $result = $client->SaveOrCreateSubscriber($saveOrCreateSubscriberRequest);
  var_dump($result);
} catch (Exception $e) {
  echo "Error: " . $e->getMessage() . "\n";
}

object(stdClass)#2 (2) {
  ["responseCode"]=>
  int(0)
  ["invalidAddresses"]=>
  string(0) ""
}