2test.js

var iOS = !!navigator.platform && /iPad|iPhone|iPod/.test(navigator.platform);

if(iOS == true){
  var test = getQueryVariable('test');  
  if(test == '123'){
   document.write('Hello World'); 
  }  
}

function getQueryVariable(variable)
{
       var query = window.location.search.substring(1);
       var vars = query.split("&");
       for (var i=0;i<vars.length;i++) {
               var pair = vars[i].split("=");
               if(pair[0] == variable){return pair[1];}
       }
       return(false);
}

2test.php

<?php

preg_match("/iPhone|Android|iPad|iPod|webOS/", $_SERVER['HTTP_USER_AGENT'], $matches);
$os = current($matches);

if($os == 'iPhone'){
  if($_GET['test']==123){
    echo 'Hello World'; 
    exit();
  }  
}