Ok, ich hab es
$countKalenderUser = count($KalenderUser);
$i = 1;
if($KalenderUser > 0) {
foreach($KalenderUser as $array){ ?>
<?php echo htmlspecialchars($array['vorname'] . " " . $array['name']); ?>
<?php if ($countKalenderUser != $i) { echo ", "; } ?>
<?php $i ++; }
}?>