Apple has officially started to reimburse iPhone 4 owners who purchased a bumper case on their own, and it looks like the rest of us can send away for a free bumper now, too.

Apple is managing the promotion through an app, available now in the App Store. Instructions are pretty simple. You download the app, sign in using your Apple ID, and select your bumper or case. As it stands you can only get one color (black) and you’re looking at a three to five week delivery window. As for time limitations, here’s the official word:

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.

Remember, you don’t have to get a bumper. You can get any of the approved cases for free as well.