jquery - Ajax call PHP Service cross domain

I'm starting developing an app and I'm having trouble with the login.

I have a form with an Ajax call to a PHP service to validate the user, I uploaded both files to my server and it works perfect. I input user and password, goes to the PHP file and validate the user, so far so good.

The problem is that these two files will be in different servers. Now I have the PHP file hosted on my server, and the form/ajax call localhost and it doesn't work.

Here's the code:

PHP:

header('Content-type: application/json');
$server = "localhost";
$username = "****";
$password = "****";
$database = "*****";


$con = mysql_connect($server, $username, $password) or die ("Error: " . mysql_error());

mysql_select_db($database, $con);

$user = mysql_real_escape_string($_POST["user"]);
$pass = mysql_real_escape_string($_POST["pass"]);

$result = mysql_query("SELECT * FROM Usuarios WHERE IdUsuario = '" . $user . "' AND Clave = '" . $pass . "'");

$numResults = mysql_num_rows($result);


echo $numResults;

mysql_close($con);
?>

JS:

$( document ).ready(function() {


    $('form').submit(function(event){
        event.preventDefault();

        var user = $(this).find("#user").val();
        var pass = $(this).find("#pass").val();

        $.ajax({
            type: 'POST',
            crossdomain: true,

            data: 'user=' + user + '&pass=' + pass,
            url: 'http://www.url.com/login.php',
            success: function(data){
                if(data == 1){
                    alert("YES!");    
                }else{
                    alert("NO");
                }
            },
            error: function(){

                alert('Error');
            }
        }); 
        return false;
    });
});

I have also tried with dataType: "json" and "jsonp"