Simple, wireless, communication tool built into the DS.
Although i think the range is very poor. 60 feet is hardly anything. No one is ever in close enough range of me or has Picto Chat switched on. I don't see the point in going to those certain Picto Chat locations just to chat over the DS. You may as well just chat with them in person. The only use i see for Picto Chat is at school during a boring class.
But it does come free with the DS, so it's not all that bad.