Image is from CNET in this article

Should we call it the iPhone or the iPhlop? Some people would argue either way with the recent signal loss troubles with the iPhone 4. The problem is people hold their phones with what is called the “Death” grip. This covers the antenna and basically blocks any signal from being detected. This one problem or as some are calling a major design flaw has slowed down the sales on the iPhone, but hopefully they will make a new iPhone 4 with less problem with reception. The best way around this problem is to use the “Angel” grip or holding your phone with your finger tips or to buy some sort of rubber case. If this doesn’t help you may consider down grading to the previous iPhone.