Well, Apple's reply pretty much confirms this is a hardware design flaw. It also indicates, to me, that this is and was a known issue to them, which they conveniently failed to mention. I don't get it... Any other company would get totally spanked for such a thing. It doesn't matter if putting a case on solves it, it doesn't matter if holding it differently solves it. It's still a company selling insane numbers of flawed products.

I just want to stress one point. It's true what Apple say - any phone can have its signal blocked when held a certain way. Earlier in the thread I wrote that if I cup my N900 in my hands really firmly in its bottom area, where the headphone jack is, I also lose reception, since that is the area where the GSM antenna is located. That's also the reason the guy in the iPhone 3G video lost reception.
There is a key difference between this and the iPhone 4 situation. You don't normally hold a phone like I did when I tried it with the N900, or even like the 3G guy did. Notice that he really grabbed it with his palm flat against the back. In the iPhone 4, however, it appears that even a touch in the wrong area kills the reception. There's no need to block anything, because the antennas are exposed and apparently shorting them works just as well.