To MessageContract or not?

Good Morning All,

I attended a user group meeting the other day on WCF, and the speaker
suggested that all operation contracts should receive and return types
decorated with the MessageContract attribute. The primary reason that
he gave for adopting this design was to aid in versioning. By
creating message contracts for both the request and response, one
could alter the message contract without having to change the service
contract. This seems like good advice. Has anyone tried this and
found that it wasn't a good idea? Does anyone have any good blog
posts or articles that they can refer me to with more info? Also,
suppose I have a number of services wich RPC-style operation contracts
and want to change them to use typed messages instead. How would I
alter them in a way that existing clients continue to work?

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Regards,

Travis Spencer