Server side code in controller:
     public ContentResult TaskJsonP(string callback,int id)
        {
            var model = service.GetTaskDetails(new TaskDetailRequest() { Id = id });
            //return Json(model, JsonRequestBehavior.AllowGet);
            return Content(String.Format("{0}({1});",
          callback,
          new JavaScriptSerializer().Serialize(model)),          
          "application/javascript");

        }
Client side you can open any page and try below:
$.get("http://localhost:45897/home/taskJsonP/1",
                  
                   function(value)
                   {
                       alert (value)              },
                   "jsonp"
             );