<?php
$origin = $_SERVER["HTTP_ORIGIN"];
header('content-type: application/json; charset=utf-8');
//header('content-type: text/plain; charset=utf-8');
//en caso de json en vez de jsonp habría que habilitar CORS:

//o bien
//;header("access-control-allow-origin: " .  $origin );
header("Access-Control-Allow-Origin: *");

echo json_encode(array(

    'field' => 'value'

));

?>