While we’ve been unable to date to create the reported conditions
in our National Testing Center in Yonkers, New York, I and a
colleague did repeatedly experience loss of signal when using an
iPhone 4 a few miles north of there today.
While in my home, I held the iPhone in my left hand, gripping it
with normal pressure. My palm covered a gap between parts of the
metal band that forms the outer ring of the iPhone and serves as
its antenna. As I did so, I moved my pinky finger to the
corresponding gap on the other side.
Almost immediately, the signal strength began to drop in the meter
from the original three or four bars — depending on my location
within the house — to zero bars. The drop took about 5 seconds.
So we seem to be nearing consensus. With strong reception, bridging that antenna gap doesn’t matter much. With weak reception, bridging that gap is enough to lose the signal.