Another code is Data Matrix (http://en.wikipedia.org/wiki/Data_Matrix) which is now having some backup from both the US Govt and the electronic industry which is planning to add extra information on top of chips and small components: these would be read by automatic assembly machines for a more reliable and foolproof assembly of boards.
PC and mobile phones encoders/decoders are available for Datamatrix as well, but I went for QR code and basta ! No, actually I tried some free Datamatrix decoders and proved less reliable, on my phone at lest, than the QR decoder I am showing here.
"QR Code is trademarked by Denso Wave, inc. as stated in Denso Wave's" this is what can be read on Wikipedia and on Denso Wave's homesite but we can read also that (http://www.denso-wave.com/qrcode/microqr-e.html) "QR Code is open in the sense that the specification of QR Code is disclosed and that the patent right owned by Denso Wave is not exercised.".
And that's great because this opens to a great deal of opportunities.
...Follow me then and you'll have Y2010 business cards also.
Note (01/02/08) :
Jaxo System's web address has moved to http://www.jaxo-systems.com (thank you, jackOjack)
Step 1: Parts needed
Some text to 2D-encode (and worth to decode !).
A PC with a Web browser and Java VM : Windows or Linux doesn't matter for the encoding process.
The decoder applet for your camera-equipped mobile (if you want to decode also, I want).
The text for me will be http://www.instructables.com and http://www.5volt.eu , the latter being the place where I post my projects I can't make an Instructable. Both worth to me to encode and print on stickers, business cards and T-shirts.
The PC can be any, equipped with a web browser and Java.
Jaxo Systems ( http://www.jaxo-systems.com/home ) makes software for image processing also and provide decoding Java applications for mobile phones and PCs to acquire and decode various bar codes (2D included) and free to download.
In their homepage you can encode your text and save the 2D representation as a graphic file ready for print.
You can also download the jar file to execute as a stand alone application.
Use is granted by Jaxo Systems for personal use only, as stated in their homepage.
Below is a roundup of addresses found by readers and posted in comments.
Many of them have downloads for mobile phones, some others have directions for others sites also.
http://www.drhu.org/ (suffering HD failure as of 31/01/08)