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 (First Class Mail brings the total to $3.73). This kind of silicon case could also help with the glass shattering. Note: Gizmodo or Gawker Media doesn't endorse or have any relationship with this company. They just posted a note in our Fix the iPhone 4 Facebook Petition Group. [Cases]