We put Steve Jobs' claims that all smartphone suffer from signal loss if held in the 'grip of death' to the test.
Unlikely death grips
Though it seems entirely plausible that an iPhone 4 user might hold the device in such a way that the grip would interfere with the antenna and reduce the phone's signal strength, the various death grips required to attenuate the antennas of the other phones we tested seem far less likely in the real world.
For instance, the death grip for the EVO 4G involves cupping your hand around the top of the phone. You wouldn't purposely hold your phone like this; it feels very awkward and makes accidentally hitting the volume buttons on the phone's spine much more likely. Even more unnatural is the death grip for the Droid X: We had to use a two hands to grasp the bottom and the top of the phone simultaneously. Other death grips, though a little less exotic, still felt decidedly artificial.
Holding your palm (or finger) over this break in the metal band around the iPhone 4's edge can seriously compromise the performance of the phone's antenna. Part of the reason the iPhone is different is that Apple built its antenna into the metal housing that forms the outside edge of the phone.
This represents a dramatic departure from the way most antennas are built into phones - namely, inside the shell and usually at the bottom of the phone. As a result, the iPhone 4's exposed antenna is much more susceptible to interference (attenuation) from the hand of the person holding the phone. This risky (and apparently not fully tested) design move now looks like an epic fail - a cautionary tale that will be retold at drafting tables for years to come.
The bottom line
Apple's assertion that antenna attenuation is a common problem on smartphones is clearly true. Every one of the phones we tested experienced some degree of attenuation when held firmly in a position that covered the device's antenna. On the other hand, our informal tests indicate that different phone models do not exhibit attenuation to the same degree - and the iPhone 4 performed far worse when attenuated than did most of its competitors in our tests. Most significantly, the iPhone 4 - almost certainly because of its 'innovative' external antenna - was the only phone we tested that has a distinct (and easily reachable) weak spot capable of ending a call with a single touch.