While Apple isn't giving away free cases to people experiencing the iPhone 4's antenna problem, a company called cases.com claims they will. They say they will give you a black, purple, rose, blue or white LifeGrip silicone-based case for free.
You only have to pay for the shipping. This kind of silicon case could also help with the glass shattering. Note: Gizmodo or Gawker Media don't endorse or have any relationship with this company. [Cases]