The kind folk at Nokia have set up a web page to let people create their own mobile phone barcodes. You can choose between the QR and Datamatrix formats, and the images can be embedded anywhere you like for people to snap and use. 

You can create mobile codes for web URLs, plain text and telephone numbers, and any camera phone with the right software should be able to read and decipher the code to deliver the information you want. I’m trying to think of a cool application for this, but all I come up with is something like a treasure hunt, sticking it on a T-shirt for party fun or boring advertising. There must be more ideas though, right?