title: WP7 : Trial mode, what if the user uninstalled the App
body: <p>I'm planning to implement a trial mode for my app, but just realised that the installation date has to be saved in the isolated storage and compared to the time limit I have set for my trial App. 
  However the user can uninstall the trial App, obviously it removes the isolated storage too and it means they can reinstall the trial app and use it again !</p>
  
  <p>What's the best way to store installation date or any kind of unique id to the phone somewhere other than isolated storage !</p>