How to pass data from one domain to another domain(cross domain) using json?‏

//Javascript code

<script type="text/javascript">

$(document).ready(function()
{

var surl =  "http://www.example.com/json.php";

email_id=document.getElementById("email").value;

$.ajax({
url: surl,
data: {email:email_id},
dataType: "jsonp",
jsonp : "callback",
jsonpCallback: "jsonpcallback"
});
});

function jsonpcallback(rtndata)
{
document.getElementById("disp_data").innerHTML=rtndata.message;
}

</script>

//json.php file code

<?php

$display="<b>HI Json</b>";

$display.="<p>HI This is testing json.</p>";

$rtnjsonobj->message = $display;

echo $_GET['callback']. '('. json_encode($rtnjsonobj) . ')';

?>