Response.Write JSONP Using JQuery And WCF?

UPDATE:

The service cannot be activated because it does not support ASP.NET compatibility. ASP.NET compatibility is enabled for this application. Turn off ASP.NET compatibility mode in the web.config or add the AspNetCompatibilityRequirements attribute to the service type with RequirementsMode setting as 'Allowed' or 'Required'.

when i try to access wcf service i get this error: the reason is HttpContext.Current is null, what should i do in this case?

Object reference not set to an instance of an object.

System.Web.Script.Serialization.JavaScriptSerializer s = new System.Web.Script.Serialization.JavaScriptSerializer();
Person p = new Person() { FirstName = "First name", LastName= "last name" };
string json = s.Serialize(p);
System.Web.HttpContext.Current.Response.Write("jsoncallback" + json);} //error