QR-Codes are those square bar-codes popping up all over the place. The reason, they can interact with Smart Phones to provide links, phone numbers and even SMS messages!
Creating one takes seconds via a site like this one, QR-Code Generator
All the other person needs is a QR reader app on their phone. The site above offers one, but I used barcode scanner for Android (as I already had it installed) and the link worked fine.
As simple and efficient way to provide instant information. Imagine working with your local museum to place QR codes around their exhibits, then send in your students on a field trip with laptops or smart phones.