Stamkey is a pc/mobile application developed by Sachihata. A tag embeds personal information into a camera-phone readable format that can be imported into mobile phones. As I don't read japanese, I rely on Josh Rubin's blog for the game comcept explanation:

The Stamkey is a stamp that you open up and creates a 2D barcode that can be scanned by a mobile phone. The data received from the barcode is personal information, which is then stored in the mobile. They say that people are placing these 2D barcodes on business cards. But really the possibilities are endless. Just think, no more standing around dictating digits for another for punch in their phone or the expected call back for proper digit exchange.