If you haven't seen it yet, check out a new site about building Drupal sites for mobile phones called MobileDrupal.com.
I was recently in Japan and wrote an article about the cell phone barcodes that are common in Japan.
After I wrote the article I found out that Google has released print ad 2D barcodes
Japan's cell phone technology is generally a couple of steps ahead of the USA. One interesting feature of Japanese cell phones is that you can take a photo of a special bar code with the phone, and the mobile phone will perform an action, like visit a Web page or send an email.