ChannelFactory<IService1> factory = new ChannelFactory<IService1>("BasicHttpBinding_IService1");

        Task<string> t1 = Task<string>.Factory.StartNew(() => { return factory.CreateChannel().GetData(2); });
        Task<string> t2 = Task<string>.Factory.StartNew(() => { return factory.CreateChannel().GetData(5); });

        Task.Factory.ContinueWhenAll(new[] { t1, t2 }, t =>
        {
            foreach (var task in t)
            {
                //get result here
            }
        });

[ServiceContract(Namespace = "X", Name = "TheContract")]//Server side contract
public interface IService1
{
    [OperationContract]
    string GetData(int value);
}

[ServiceContract(Namespace = "X", Name = "TheContract")]//client side contract
public interface IService1Async
{
    [OperationContract]
    string GetData(int value);

    [OperationContract]
    Task<string> GetDataAsync(int value);
}

ChannelFactory<IService1Async> factory = new ChannelFactory<IService1Async>("BasicHttpBinding_IService2");

        var t1 = factory.CreateChannel().GetDataAsync(2);
        var t2 = factory.CreateChannel().GetDataAsync(5);

        Task.Factory.ContinueWhenAll(new[] { t1, t2 }, (Task<string>[] t) =>
            {
                foreach (var task in t)
                {
                    //get result here
                }
            });