Jailbreak app CallLock is helpful to avoid iPhone 4 proximity sensor issue by locking the device screen during the call. It help by halting you to mistakenly press buttons that may dial, hangup pr hold a call. Users who are experiencing proximity sensor issue with their iPhone 4 device must use this app.
CallLock app will overwrite the by default control of Power button while you are calling to lock the screen instead of end call control. The app can be enabled automatically from the settings which means it will not create an extra icon at your home screen to annoy you. The app works both for incoming and outgoing calls automatically.