With updated version this app acquired such features as user-reviewed listings for restaurants, bars and banks etc. using iPhone’s GPS connection for reaching your friends.
In addition this app contains a new augmented reality feature called “Monocle”. It shows you what’s nearby when you turn round with your iphone’s camera. These kinds of applications being under development wait for the release of the iPhone OS 3.1 to officially enable the feature. This explains why the augmented reality feature in the Yelp application was included as a hidden Easter egg to avoid detection by Apple's reviewers.
As soon as you download an updated Yelp app (which is by the way FREE) you must shake your iPhone three times to activate a feature “Monocle”. A message in form of a blue box will let you know if the feature has been activated. When the button appears in the top right corner you will be able to use it. But you should take into consideration that it works only with iPhone 3GS.