Jquery's cross domain ajax call

Jquery:
$(document).ready(function() {
var surl = "http://www.yoursite.com/webservice.asmx";
$.ajax({
type: 'GET',
url: surl,
crossDomain: true,
contentType: "application/json; charset=utf-8",
data: { MemberID: 1054 },
dataType: "jsonp",
success: function(msg) {
$.each(msg, function(name, value) {
alert(value);
});
},
error: function(xhr, status, error) { alert('Servidor de error 404 !!'); },
async: false,
cache: false
});
});

    [WebMethod]
    public void JsonPTest(int a, int b)
    {
        int original_result = a + b;
        var context = HttpContext.Current;

        // Prepare
        string callback = context.Request.Params["callback"];
        string json = "{c: " + original_result + "}";//Newtonsoft.Json.JsonConvert.SerializeObject(...);
        string response = string.IsNullOrEmpty(callback) ? json : string.Format("{0}({1});", callback, json);

        // Response
        context.Response.ContentType = "application/json";
        context.Response.Write(response);
    }