At the Rochester, Ind., Dairy Queen, more than 350 customers can wave special stickers fixed to the backs of their cell phones at a scanner in the store, thereby banking loyalty points and qualifying for free cones and Blizzard sundaes. Customers have come back to the store more frequently as a result, helping sale rise more than 3 percent in the past year, says co-owner Dave Reasner. "It's something that's working," he says.