According to patentlyapple, Apple filed a patent that reveals the use of gesture controls of 'swiping' and 'tapping' the built-in camera on the back of the phone. Not only does this visually free the display from your fingers, it also opens a whole new realm of gesture controls.
(click image to enlarge)
For example, during access of a voice mailbox, the user may swipe his finger in the direction of the arrow 120 over the lens to rewind the playback of a voicemail message. The user may swipe his finger over the lens in the direction opposite the arrow to fast forward the playback of a voicemail message.
I'm curious to see when and if this will make it to a future iPhone...