Here's a quick list of which Apple devices can run iOS 5, required for the app:
- iPhone 3GS
- GSM/CMDA iPhone 4
- iPhone 4S, iPod Touch 3rd and 4th Generation
- all iPad
If the app doesn't work on the devices above, the likely scenario is that the operating system has not been updated to iOS5. The update to iOS5 must be done via iTunes. Only updates above iOS5 can be done by wifi.
Here is a link to plain english instructions on updating from 4 to 5: http://iphoneheat.com/2011/10/update-ios-5-iphone-ipad-ipod-touch
If the device is not on the list above, it will not work with iOS5 or the app.