the iPhone unit I’ve been reviewing. I can’t even reproduce it, no matter how hard I try. I’m sitting here right now. I’m wrapping my hand every which way — I’m even holding it with two fists, completely concealing the silver band around the edges — and my four-bar signal strength doesn’t waver. On Twitter, most of my followers seem to indicate the same thing; it’s a problem that just doesn’t exist for them," Pogue reports. "But clearly, the problem exists for some people. PC Magazine, for example, has been able to reproduce the problem. For them, it happens only if (a) your hand is somewhat sweaty and (b) you hold the phone in such a way that your fingers are covering all three black gaps in the stainless-steel band around the phone’s edge. (For this reason, left-handers seem to be the most-affected population.) In that configuration, signal strength drops a little."
http://pogue.blogs.nytimes.com/2010/06/25/the-mystery-of-the-iphone-death-grip/