This application allows you to fake all manner of activities on your WP7 handset, hopefully to the amusement of all 🙂 .
The app currently has 5 (fake) features:
1. Blue screen of death
2. Make fake calls
3. Turn your phone into a Geiger Counter
4. Make fake check pictures
5. Make police siren sounds, accompanied with lights
The developer promises to add more, likely fake, features in the future.
This application is free, you can download it at Marketplace here.