Yesterday, we posted information about Metro Paris Subway application for iPhone 3GS, which was one of the first applications to bring augmented reality to the iPhone platform. And, now the latest update of Yelp’s iPhone app features augmented reality Easter egg called “Monocle”. To activate Monocle shake the iPhone 3GS three times, a message will appear on the screen stating “the Monocle has been activated”. Once the Monocle is activate it allows users to see business ratings overlaid on the video stream from their iPhone camera.

As Monocle needs both GPS and compass to work properly it will only work with iPhone 3GS. It is believed that this Easter egg will become a feature of Yelp app when Apple releases iPhone OS 3.1, which would allow complete access to compass on iPhone 3GS. We have added a video below showing Yelp Monocle in action.
[Via MacRumors]