callscreen.php

<?php
  $numbers = array("<number to call n>", "<number to call n>", "<number to call n>");
  $number_index = isset($_REQUEST['number_index']) ? $_REQUEST['number_index'] : "0";
  $DialCallStatus = isset($_POST['DialCallStatus']) ? $_POST['DialCallStatus'] : "";
  header("content-type: text/xml");

  if($DialCallStatus!="completed" && $number_index == 2){
   $number_index = 0;
  }

  if($DialCallStatus!="completed" && $number_index<count($numbers)){
?>
 <Response>
  <Dial callerId="+8150xxxxyyyy" timeout="10" action="callscreen.php?number_index=<?php echo $number_index+1 ?>">
   <Number>
    <?php echo $numbers[$number_index] ?>
   </Number>
  </Dial>
 </Response>
<?php
 } else {
?>
 <Response>
  <Hangup/>
 </Response>
<?php
 }
?>