Consumer Reports has reviewed the iPhone 4 and the news isn’t good for Apple:

It’s official. Consumer Reports’ engineers have just completed testing the iPhone 4, and have confirmed that there is a problem with its reception. When your finger or hand touches a spot on the phone’s lower left side—an easy thing, especially for lefties—the signal can significantly degrade enough to cause you to lose your connection altogether if you’re in an area with a weak signal. Due to this problem, we can’t recommend the iPhone 4.