People have started to receive the free cases that Apple are providing to iPhone 4 users.
If you haven't already applied for a case, you can so at www.apple.com/iphone/case-program.
The procedure is very quick and easy. You simply download and run an app from the above page. This will present you with a list of cases to choose from. Once you have made your choice, you simply need to confirm your mailing address. The app is perfectly accessible with VoiceOver.
Unfortunately, if you haven't already applied, you are likely to face quite a delay before you actually receive your case.