I would like to see the example you are talking about, as it sounds like the example sends objects with behavior across the wire rather than just models (or messages, if you would prefer a better SOA term).
When you send an object that is formated as a data model, or message, it will not contain methods to use. And, with interop, it does not make a lot of sense to set up behavior (methods) to go across the wire.
As for what you can do, since you are serializing, you can create the behavioral methods, if they make sense on your side. Personally, I would create the behavior in other objects and keep the models/messages as state containers. But, your mileage may vary. ;-)