Anand Shimpi, Anandtech (Raleigh, North Carolina): "I can make the signal drop, but that's not because I'm some sort of superhero - anyone can make the signal drop on their iPhone 4, iPhone 3GS, Nexus One, etc... The iPhone 4 simply drops "more of its signal" than other phones, depending on how you hold it, because of the location and design of the antenna.
So to summarize, yes I can make the signal drop and it has led to dropped calls or trouble continuing the call. It's particularly bad in my office if I hold the phone "incorrectly" while texting or using the phone in portrait mode for something else. Luckily I'm on WiFi when I'm using it like that so it's normally not as big of an issue.
Ultimately it is a real problem with the iPhone 4 and will impact those who have borderline AT&T network coverage more than those who have great coverage. When Apple pushes this new fix forward it's really going to show people whether they have good signal or bad signal where they live (hopefully)." (Make sure you check out Anandtech's full report on the signal issue, as well.)