In my previous post, Building an RSS Reader for Windows Phone 7, you may have wondered how I was able to reference SyndicationFeed as this class is in the System.ServiceModel.Syndication namespace which isn’t available in the default list of references for a new Windows Phone 7 project, nor is this assembly in the list of .NET assemblies when you do Add Reference.
The secret is that you need to add a reference to the desktop Silverlight v3 assembly, C:Program FilesMicrosoft SDKsSilverlightv3.0LibrariesClientSystem.ServiceModel.Syndication.dll. This will get deployed along with your application, giving you access to the Syndication namespace.
Happy RSS Reading!