We made an iPhone app called "Helloscan" for a client.
The app allow you to scan a code (barcode or QR Code) and to query your server (database, open source CMS, anything you want) and display the result in the app.
For now there is almost no english documentation but the app and scripting is very easy to understand if you know programming.
Here is some example uses of Helloscan :
- Stock management in Prestashop, Magento, Virtuemart or other Open Source CMS
- Add product in your database with Google Shopping API
- Query SEOmoz API with QR Code
- Event invitation card management
- etc.
There is already some script available for server (Php for the langage) but you can make anything you want.
You can read an english tutorial here :
Prestashop, Magento and Virtuemart barcode scanner (and much more !)
Or french tutorial (SEOmoz API query) :
Faire un rapport SEO au supermarché avec les QR Code
Helloscan app cost $5,99 : App Store - HelloScan
Some other ressources :