$client = new SoapClient($wsdlUrl);
$backclickStatisticRequest = new StdClass();
$backclickStatisticRequest->mandatorId = 0;
$backclickStatisticRequest->newsletterIds = array(1);
try {
  $result = $client->BackclickStatistic($backclickStatisticRequest);
  var_dump($result);
} catch (Exception $e) {
  echo "Fehler aufgetreten: " . $e->getMessage() . "\r\n";
}

object(stdClass)#3 (1) {
  ["backclickStatistic"]=>
  object(stdClass)#4 (22) {
    ["sendedByInternalMta"]=>
    bool(true)
    ["usedConversionTracking"]=>
    bool(true)
    ["abTest"]=>
    bool(false)
    ["newsletterListName"]=>
    string(15) "Testverteiler 1"
    ["newsletterSubject"]=>
    string(22) "Newslettertest"
    ["newsletterDescription"]=>
    string(22) "Newslettertest"
    ["newsletterId"]=>
    int(1)
    ["newsletterListId"]=>
    int(1)
    ["sendStartTime"]=>
    string(29) "2012-10-29T11:13:00.000+01:00"
    ["numRecipientsUnadjusted"]=>
    int(6)
    ["numRecipientsAdjusted"]=>
    int(3)
    ["numSend"]=>
    int(0)
    ["numDelivered"]=>
    int(3)
    ["numLinksClicked"]=>
    int(0)
    ["numOpened"]=>
    int(0)
    ["numUniqueOpened"]=>
    int(0)
    ["numBackclicks"]=>
    int(0)
    ["numUniqueBackclicks"]=>
    int(0)
    ["numActiveSuscribers"]=>
    int(0)
    ["numConversionTracking"]=>
    int(0)
    ["numGeneratedComplaints"]=>
    int(0)
    ["summaryCount"]=>
    int(1)
  }
}