$.ajax({
 type: "GET",
 url: "http://www.xxx.com/Rest/ValidAccountsExists.aspx?accounts=admin",
 dataType: "jsonp",
 jsonp: "jsoncallback",  
 success: function (result) {   
 alert(result.Success);   
 alert(result.Content);                               
 },

 error: function (result, status) {
    //處理錯誤
 }
});

string accounts = GameRequest.GetQueryString("accounts");
string jsoncallback = GameRequest.GetQueryString("jsoncallback");
Response.ContentEncoding =System.Text.Encoding.UTF8;
Response.ContentType = "application/json";
Response.Write(jsoncallback + "({/"Success/":/"True/",/"Content/":/"" + accounts  + "/"})");
Response.End();