title: WP7 perform navigation from outside a PhoneApplicationPage
body: <p>I am developing a WP7 app, that consumes RESTful web services and uses login. I have a utility class for retrieving the actual data.</p>
  
  <p>Whenever a certain result is received I have to perform a new login, and thus have to display the login screen to the user.</p>
  
  <p>Is it possible from this utility class to force the app to navigate to some specific page? Possibly through the <code>App</code> instance?</p>
  
  <p>Thank you!</p>