This was the new feature that was developed by the HTC phones that you can control your phone with gestures. The feature was limited to HTC phones for some time and nobody thought of introducing it to the iOS. Gesture controls were missing in iPhone but here is some app using which you can use these features on your iOS device too.
Turn to Hangup is an app introduced by Cydia for their users that enable the users to use their iPhone to silence or reject any incoming call using some gestures like you can flip your iPhone to silence the call or shake it to reject it. Although you can do the same using the Power button on the iPhone, but doing this using the gestures is little exciting.
All you have to do is just visit the Cydia on your jailbroken iPhone, search for Turn to Hangup, and install it. This will install the app in your phone which takes nothing more than 58KB of the disk space. This will also provide you with the option of turning off the feature which is enabled by default. The download is freely available on the BigBoss repo of the Cydia store.
To see how this app works, just flip the phone the next time you receive a call and it will be rejected automatically. Although the app says to use this feature on some flat and rigid surface, but this works pretty well on other surfaces too.
The app also enables you to silence an incoming call just by shaking it. So next time if you wish to silence a call, just shake it instead of pressing the power button once.
So you can search the app from the Cydia store and install it on your iPhone.