The UPC you find on packaging is a one-dimensional barcode that's been in use, in one form or another, since the 1970s. While its a good symbology to encode numbers like a product identifier, its not really big enough to hold much more. It also requires a barcode scanner (like those connected to the POS), although iPhone apps like RedLaser have proved a mobile camera can be made to work in many situations.

The next generation barcodes are two-dimensional and therefore capable of holding much more information as well as being more conducive to cameras. The most popular format is the QR Code, widely used in Japan because almost every mobile phone has a built-in reader.

A typical use for QR Codes is to embed a URL so that that a mobile phone can quickly navigate to the specified web page. QR Codes can be found on posters, billboards, catalogs, and circulars. Speaking of which, Best Buy recently put a QR code in their circular as shown below.

If fact, they even updated their iPhone application to include a QR Code reader. I was able to scan the barcode above right from the screen with my iPhone without issues, even though its fairly small in this image. Clearly they are planning to incorporate more QR Codes in their stores and advertising.

If you haven't seen QR Codes before, you're not looking hard enough. They are around and will continue to spread.