The iPhone 4 is out, and of course I had to run out and buy a couple of them. Almost immediately I noticed something was wrong with both of them. If you touch the iPhone 4 in the right spots, the 3G coverage diminishes, and can even drop off completely. The video below demonstrates what happens, and how to duplicate the issue.
Essentially, there are seams that separate the various antennae that the iPhone 4 uses, famously illustrated in this pic during the WWDC 2010 conference:
As you can see from the video, holding the seams in the right spot causes an instant 3G signal loss. Removing your fingers from the seams results in an instant signal recovery. I won’t pretend to know the physics of what is going on here, but at best guess it seems that when you hold the bottom seams (probably specifically the left seam, but in my experimentation, holding both sides yielded the greatest loss of signal strength), it ‘completes a circuit’ with the other antenna and causes interference. Strange stuff.
Either way, I’m sure a snazzy expensive silicone bumper case would prevent the issue… it’s just sad that it’s essentially required now if you expect decent 3G coverage with the iPhone 4.
urban tornado 
Lol. I just replicated this. Shit. So what would a phone cover do? Would it continuously diminish the signal. How gay.
Need a non-conducting cover to wrap around the edges… hence, Apple’s own silicone bumper case. MORE MONEY FOR APPLE! Such bastards!