First introduced a few years back by a couple of ITP (Interactive Telecommunications Program) students, the cleverly named Socialight, a free service using social networking to deliver localized info to your mobile phone, launched in London today. Like a combination of Dodgeball and Google 411, The service works by geo-tagging places with "stickies" that list the particulars of a favorite bar (for instance), which then can be accessed by other users who use the mobile web app or who text a query. Socialight figures out where you are using network-positioning services, providing pinpointed details.
You can also simply configure your mobile to notify you of nearby stickies posted by friends or the entire community, so that you automatically navigate an area like an insider. The data lives on a website as well and "channels" curated by celebs and publications (such as Anthony Bourdain and Monocle) and others provide a richer experience.