Turn to Hangup is a new tweak by developer Jose Fidalgo Hidalgo that lets you turn your iPhone face down to dismiss incoming calls.
This tweak allows to hang up the incoming calls simply by turning the device face down on a flat surface. Also allows to shut up the ringing/vibrating by shaking the device. Follow me on twitter @josfh2005 to receive updates about this tweak and more to come.
The tweak can be enabled/disabled from the Settings.app and downloaded free from the Big Boss Cydia Repository.