WPF

[ServiceContract]
public interface ITestContractCallback
{
    [OperationContract(IsOneWay = true)]
    void CallBackFunc();
}

[ServiceContract(CallbackContract=typeof(ITestContractCallback))]
public interface ITestContract
{
    [OperationContract(IsOneWay = false)]
    ulong GetValue();
}

[ServiceBehavior(InstanceContextMode = InstanceContextMode.PerSession)]
public class Server : ITestContract
{
    public static ITestContractCallback _callback;
    public Thread _callbackHammererThread;

    public Server()
    {
        _callback = OperationContext.Current.GetCallbackChannel<ITestContractCallback>();
        _callbackHammererThread = new Thread(CallbackHammererThread);
        _callbackHammererThread.Start();
    }

    public static void CallbackHammererThread()
    {
        while (true)
        {
            if (_callback != null)
            {
                _callback.CallBackFunc();
            }
            Thread.Sleep(1);
        }
    }

    #region ITestContract Members

    public ulong GetValue()
    {
        return 100000;
    }
    #endregion
}

class Program
{
    static void Main(string[] args)
    {
        NetTcpBinding binding = new NetTcpBinding();
        ServiceHost host = new ServiceHost(typeof(Server));
        Uri BaseAddressString = new Uri("net.tcp://localhost:1337/test");
        host.AddServiceEndpoint(typeof(ITestContract), new NetTcpBinding(), BaseAddressString);
        host.Open();
        Application.Run();
        host.Close();
    }
}