What's all this then?
QR Codes are a two-dimensional barcode, designed to be read by mobile phones. They can hold small amounts of data such as URLs, phone numbers, plain text or whatever you like. They're pretty cool, since you can leave links lying around in the real world where people can find them and go online instantly to see what they contain.
If you're in possession of one of my newer business cards, there's a QR code on the back. This contains a Vcard, which contains my name, phone number and email address. A VCard is a standard file format that should be accepted by most address books, and your phone should offer to store the information as a new contact.
You will see individual QR codes alongside each of the aviation images on this site, too. The codes contain a link to a mobile version of the page. If you see your plane on my site, use the QR code to bookmark it to your phone instantly!
BIG thanks to Y.Swetake for the code to generate QR images dynamically!
I've tested this with my Sony Ericsson (a standard Java phone) and an Apple iPhone and it works on both. Can't speak for every device though.
So how do you read them?
You can get reader software via mobile-barcodes.com. I recommend the Kaywa reader as it's the only one that (a) doesn't crash horribly and (b) keeps a history.
Want to make your own?
There's various websites with QR creator applications, which are fine if you want to make a plain URL or similar. However, phones like my Sony Ericsson can only interpret QR codes that are relatively simple. If you're encoding a VCard, it can quickly get to be too much data for the phone to handle. The only creator that I have found which will create a VCard readable by both Sony Ericsson and iPhone is the one at tag.cx.