The use of QR codes has wide reaching and simple application to so many uses. You do not need a 3G phone, just as long as the one you have has a camera and can access the internet, and I reccommend Opera Mini for your browser for this, then you can download the reader from I-nigma and away you go.
This one is quite big. The codes can contain pictures, maps, any information you want to include. Try this one and let me know how you get on. Keep your camera/phone at least 10 cm away from the screen, the bigger the code image, the further away you will be. Keep it as steady as you can, get the image so it has a white border round it. Wiggle round till the image is flat on your phones' screen and click.