According to a trusted source, there are multiple points on the iPhone 4’s frame for antenna reception. Our source says that the issues “can and will” be addressed by tweaking, balancing, and/or redistributing antennae reception and/or signal strength display via software. When asked if it could be a hardware issue, our source said, “Don’t be silly. It’s not the hardware. Apple’s too smart for that. In fact, most any hardware maker is too smart for that.”
via macdailynews.com
iOS 4.0.1?
The Small Wave. 
Apple resolved this problem with the iPhone 3G and I am confident that my new iPhone 4 will have a fix soon. Although, I must say, it only happens on mine when the bottom left corner is touched, but it does still happen. Also, the iPhone 4 is an amazing device. It makes my 3G look and feel very, very old. And the screen, well, it looks like it was finely painted onto the glass.