Every smartphone has a cellular antenna. And nearly every smartphone can lose signal strength if you hold it in a certain way.
The opposite of amplification, attenuation happens whenever a signal is obstructed. All antennas — including television, radio, GPS, and cellular antennas — can experience attenuation. And with most antennas, the density and composition of the human hand can cause attenuation to a greater degree than some other materials. On a mobile phone, signal loss typically occurs when your hand attenuates the most sensitive part of the antenna.
Apple has posted a video showing how the Motorola Droid X drops signal when held a certain way.Check out the video below.
Thanks to iclarified , apple