I managed to build a readable QR Code (a 2D barcode) with my Lego blocks:
The encoded content is the URL of this blog, http://murfy.de. As you can see, I had not enough black pieces, and improvised with blue. I had to fill the background with white pieces to make it readable.
You can try reading it yourself, here’s an adjusted photo that’s easy to read:
Of course, this has been done before :)
2D barcodes make it easy to read data from print-media into your cell phone, which is ideal for promoting websites or sharing contact data. With the right visual conditions and good hard- and software, you just move your camera over the code, and the information is decoded.
I am using QuickMark on the iPhone to read bar codes. It works quite well, but costs $1.99 (1,59 €). There are many other barcode readers as well, which I haven’t tested.