My Smartphone Sent Me How savvy businesses are finding customers on Foursquare, Twitter and Meetup

When someone walks in to The Coffee Groundz in Houston and demands a free coffee because they are "mayor," general manager J.R. Cohen asks to see the person's cell phone. If that makes any sense to you, you're probably familiar with the urban social media phenomenon foursquare.com.

Foursquare is best described as a mashup of Facebook, Twitter and real-life meet-ups. Users can "check in" from their locations and also see where other Foursquare contacts are lurking. The person who checks in the most from a particular spot is named "mayor" of that spot. "We have people challenging each other all the time to be mayor of Coffee Groundz," Cohen says. "We've definitely seen an increase in business, and offering something free to the mayor has become a great game."

It's yet another brilliant marketing strategy to emerge from social media: In addition to Foursquare, Twitter users "tweet up" to get together and Meetup.com is all about organizing the face-to-face--which makes them all opportunities for businesses to attract more traffic, says marketing consultant Alan Wolk, who blogs at tangerinetoad.blogspot.com. Wolk says the key is to get in the conversation and offer something to those potential customers.