Flip2Mute is a small, free application for Windows Phone which can currently run on WVGA resolution Devices such as the HTC HD2, HD and Touch Pro2 and that will change your ringer profile to silent or vibrate as well as turn off the screen when the phone is faced down by using G-Sensor polling to get the device orientation.
Current features include Mute/Vibrate the phone when it’s faced down, turn the screen off when the phone is faced down as well as allows user to change current profile with a single tap.
Just install the application to your Device and configure it via Flip2Mute Config. For uninstalling, run Unload Flip2Mute and remove the application the usual way.
(Source: XDA Developers)