QR Voice mentioned by a few other bloggers recently so I had to check it out for myself. QR Voice is a free tool that allows you to create QR codes that when scanned will play a short audio message. To create your message and QR code you can record a voice message by clicking the microphone icon on QR Voice or you can type in your message. Either way you're limited to 100 characters. QR Voice is offered in Spanish, English, Japanese, and Portuguese.
I initially had trouble getting my messages to play back correctly, but after clearing the cache on my tablet's browser QR Voice worked as it should. The app that I'm using to scan and decode QR codes is QR Droid.
Applications for Education
Teachers could use QR Voice to create QR codes that they then print and attach to objects in their classrooms or schools. Then have students try to identify those objects in the language that they're trying to learn. To check their answers students can scan the QR code and hear the correct answer on their phones or tablets.