Check this post of Gunnar Peipman in which he talks about using the web browser control in Windows Phone 7 to display RSS data.
In my posting Windows Phone 7 Series development: reading RSS feeds I showed how to read RSS feeds using XmlReader. Although I hoped to start pimping up user interface I found some more work that needs to do be done. In this posting I will show you how to use WebBrowser control to display RSS content. Example solution is also here for download.