You need to configure the WCF service to execute under the Windows logged-on identity of the calling application
You need to ensure that all clients calling GetMessage will retrieve the updated string if the message is updated by any client calling PutMessage
You need to create a channel factory that can send messages to the endpoint listening at net.pipe://localhost/ContosoService
You need to implement the error handling code for SearchMessages and create a new channel on the client only if the channel faults