Implement Asyn WCF using Task in .Net 4.0

In Fx 4.5 Task can be returned but in Fx 4.0, task can only be on Server:

    public interface IService1
    {
        [OperationContract(AsyncPattern=true)]
        IAsyncResult BeginGetDataAsync(int value, AsyncCallback cb, object state);

         string EndGetDataAsync(IAsyncResult ar);
    }

         string GetData(int value)
        {
            Random r = new Random();
            Thread.Sleep(TimeSpan.FromSeconds(3));
            return r.NextDouble().ToString();
        }

        public IAsyncResult BeginGetDataAsync(int value, AsyncCallback cb, object state)
        {
            var t = Task<string>.Factory.StartNew((s) => { return GetData(value); },state);  // must pass state into Lambda
            return t.ContinueWith(res => cb(t));

        }

        public string EndGetDataAsync(IAsyncResult ar)
        {
            return ((Task<string>)ar).Result;
        }


Client --- need to add Servicew Ref with support of async WCF checked

            object state = "";
            ServiceReference1.Service1Client c = new ServiceReference1.Service1Client();
           

            int NUM = 10;

            Stopwatch sw= new Stopwatch();
            sw.Start();

            Parallel.For(0, NUM, (ls) =>
                {
                    //for (int i = 0; i < NUM; i++)
                    //{
                    var t = Task<string>.Factory.FromAsync(c.BeginGetDataAsync, c.EndGetDataAsync, 10, state);
                    string s = t.Result;
                    Console.WriteLine(s);
                    //}
                });

     
            c.Close();
            sw.Stop();
            Console.WriteLine(sw.ElapsedMilliseconds);
            Console.ReadLine();