There's a lot of confusion about this problem. It seems to come about when conductive human skin bridges the gap between the two antennas in the lower-left corner of the phone.
I've seen it suggested that it's actually a software problem. Supposedly the reception is actually fine, but bridging that gap confuses the phone into thinking the signal is weaker, sometimes to the point where it thinks it has no signal and drops a call. If that's true, we can expect a patch addressing the issue before too long.
The iPhone 4 apparently uses new software that switches cell towers based on congestion, rather than signal strength, in an attempt to mitigate AT&T's notoriously bad service in some areas. Perhaps bridging the antennas creates some weird interaction in this software that results in needlessly switching towers.
Some iPhone 4s don't seem to exhibit the problem at all, which it seems to me would point towards a hardware defect.
Whatever the exact nature of the problem, the quickest do-it-yourself fix is to get a case so that your hand won't bridge that gap.
"The worst part about these reviews is they are [subjective]--and their scores often depend on how drunk you got the media at a Street Fighter event." — Mona Hamilton, Capcom Senior VP of Marketing
*Image indefinitely borrowed from BrainBoxLtd without his consent.
