When you use $.getJSON on an external domain it automatically actions a JSONP request, for example my tweet slider here
If you look at the source code you can see that I am calling the Twitter API using .getJSON.
So your example would be: THIS IS TESTED AND WORKS (You can go to http://smallcoders.com/javascriptdevenvironment.html to see it in action)
//JAVASCRIPT
$.getJSON('http://www.write-about-property.com/jsonp.php?callback=?','firstname=Jeff',function(res){
alert('Your name is '+res.fullname);
});
//SERVER SIDE
<?php
$fname = $_GET['firstname'];
if($fname=='Jeff')
{
//header("Content-Type: application/json");
echo $_GET['callback'] . '(' . "{'fullname' : 'Jeff Hansen'}" . ')';
}
?>
Note the ?callback=? and +res.fullname