If you are looking for one tweak to reject calls by simply changing the position of the iDevice, or to deactivate vibrations/turn off the ringtone by simply shaking the terminal, then Turn to hangup is what you are looking for. This tweak released last night in Cydia allows you to reject calls by simply placing a IPhone with the screen towards the table and allows you to deactivate the vibrations/turn off the ringtone by simply shaking the terminal.
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.
Turn to hangup is available for free in Cydia, in the BigBoss repo, and in the Settings application you can find a menu that allows you to activate it.
