Here is the e-mail I got. So if you got the phone download the app and pick the case you want. I got a free $30.00 case .

Dear iPhone 4 owner,
You are eligible to receive an iPhone 4 Bumper or a select third-party case from Apple at no charge.
Follow these steps to apply for a Bumper or case:
1.
Download the iPhone 4 Case Program app from the App Store.
2.
Launch the app on your iPhone 4 and sign in using your iTunes Store account.
3.
Select your Bumper or case.
For iPhone 4 purchases made before July 23, 2010, you must apply no later than August 22, 2010; otherwise, you must apply within 30 days of your iPhone 4 purchase. To qualify for this program, you must purchase your iPhone 4 by September 30, 2010.