Foursquare (CHECK IN FIND YOUR FRIENDS UNLOCK YOUR CITY)

How to Unlock Your World With Foursquare

                                                       
Foursquare is an online service that lets you share your current   geographic location with your friends using your mobile phone or even a   desktop web browser.
If you are in the US, you can also update your location on Foursquare   through a text message. You can use foursquare anywhere in the world.
The foursquare apps for iPhone, Blackberry, Android and Palm use GPS   to show a list of nearby places. If you've been to a place more than   anyone else, you are known as the "The Mayor" of that place.

Ya! This is absolutely free aps.. You can download it directly from ur mobile.. Enjoy