At the Antennagate press conference to address the iPhone 4′s attenuation issues in July, Steve Jobs announced of giving away free bumpers. "We now know that the iPhone 4 antenna attenuation issue is even smaller than we originally thought," Apple said in a statement posted on their site announcing a formal end to the iPhone 4 Case Program. "A small percentage of iPhone 4 users need a case, and we want to continue providing them a Bumper case for free. For everyone else, we're discontinuing the free case program on all iPhone 4s sold after September 30, 2010."
Apple also note that "We're returning to our normal returns policy for all iPhone 4s sold after September 30. Users experiencing antenna issues should call AppleCare to request a free Bumper case."
If you purchased an iPhone 4 before Sep 30, 2010, follow these steps to receive an iPhone 4 Bumper or a select 3rd-party case from Apple at no charge.