Apple today announced that under certain conditions the new ultracompact Apple USB power adapter’s metal prongs can break off and remain in a power outlet, creating the risk of electric shock.
Apple has received reports of detached prongs involving a very small percentage of the adapters sold, but no injuries have been reported.
Customer safety is always Apple’s top priority so it has voluntarily decided to exchange every ultracompact power adapter for a new redesigned adapter, free of charge. For more details on the exchange program please visit www.apple.com/support/usbadapter/exchangeprogram.
Check to see if your adapter has a green dot like the one pictured here [tuaw.com]; if so it is already up-to-date and does not need replacement.
I just purchased a new 3G phone about a week ago from my local Apple store, and the adapter does not have a green dot, so I'm not sure how recently you would have had to purchase the phone to get a new adapter.