I predict this will be the #1 Lifestyle Free app momentarily...
iPhone 4 Case Program is a free app that makes sure you are eligible for a free Bumper or a selection of third party cases.
The app is pretty straightforward. It makes note of your device's ID and iTunes ID and you select which case you want. I'm still not sold on the Bumper, as I prefer protection all around, and there will probably be a lot of Bumpers on eBay in the near future!
If you have an iPhone 4, go get the app and go get your case!
[UPDATE Apple has the ability, apparently, to hide reviews for an app and they have done so with this app. You can't even write a review... I originally wrote one, the day the app came out, but that ability has been taken away. Presumably, users were venting their frustration. I'm guessing they also made the app ineligible for rankings, as it must be very popular among iPhone 4 owners!]