Apple and Steve Jobs today announced that they will give out a Bumper case to any iPhone 4 owner. If you purchased a bumper case you will get your money back and of course you will get to keep your Bumper case. Apple is doing this in order to keep their customers happy while they experience signal issue due to the iPhone 4's antenna. Currently you cannot purchase the Bumper cases on Apple's online store, instead you will see a note saying "Apple will offer a free iPhone 4 Bumper or other select cases to iPhone 4 customers." More details on how to order you free Bumper case will be up on Apple.com next week. You can already try getting your money back right now if you have purchased a Bumper case. It's safe to say that there have been reports of iPhone 4 users who have never had any signal issues. Apple said that they cannot guaranty that everyone will be able to get a free Bumper but instead they will offer other select cases.
Source Apple Press Conference