Remember back in 2010 when there was the big hoopla over the iPhone 4's antenna? And Jobs' infamous quote "Just avoid holding it in that way,"
While it was clearly an issue with the iPhone 4, the phenomenon affected other phones as well.
Recently I was playing with the GPS in my Skyrocket. I noticed that the accuracy varied significantly depending on where I held the phone.
In this screen capture I was holding the phone at the bottom. And, yes, I was on an airplane.
The accuracy is 10 feet. Pretty good at 40,000 ft. and 470 MPH.
Then I moved my hands to cup the phone at the top. Accuracy quickly dropped to several hundred feet.
The number of satellites in use didn't decrease and the signal to noise ratio didn't change dramatically.
I wouldn't jump to the conclusion that this change in hand position affects the cellular signal in the same way. Still it is interesting.