universal contract WCF web service, OperationContract

Question

I have defined OperationContract as such in Interface.

[OperationContract(Action = "*")]
Message ProcessMessage(Message message);

On Program.cs, when I call

ServiceReference1.Service1Client o = new ServiceReference1.Service1Client();
msgafterprocess = o.ProcessMessage(msg);

Getting Error ProcessMessage, does not exist in the current context. Please tell me, is it some syntax error? Or I have misunderstood the accessibility of

[OperationContract(Action = "*")]  

when calling from client side.