According to Gizmodo, a few of their readers are reporting that after visiting the Apple store and getting their iPhones replaced, the issues they experienced with reception are completely gone. They also claim that the new iPhone looks a bit different than their old one, and that the proximity sensor is more accurate.
Not everyone has seen a problem with the iPhone 4, but those who have are getting them replaced with new ones that don’t have the issues. Whether or not this is that Apple actually fixed the issue, or that these people were imagining their problems isn’t certain. What is certain though, is that Apple has made their disgruntled customers happy. That’s a good thing.