What's hot among kids in Tokyo: playing tag using DS pictochat. They use the portable console to communicate who's the current tagger in the chaotic Tokyo back street or in the shopping mall.
Pictochat wireless signal is only available within 30 meters (= 100 feet) so in order to get the information from your buddies you need to get close, that makes you at the risk of being caught by the tagger. Sometimes the tagger can fake their identity on the chat network like "I saw the tagger in XXX". That's absolutely smart.
Sounds kind of like the world of Dennou Coil, doesn't it? Kids always are more creative than people who actually created the device. Genius.