I seem to have lost the "signal problem" My bars won't decrease no matter how I hold the iPhone.
Not quite sure what I did though...
It is psychology. First, you want your phone to work, right? Second, it only doesn't work if you hold the phone in a certain way (I think it is fingers across the gap between the two antenna halves, and sweaty fingers likely make it worse). So you may have had the problem when you got the phone first. Then you held it slightly different and the problem went away. Your brain remembers this; once your subconscious mind has figured it out, you will start _always_ holding the phone in a way that doesn't cause problems.
On the other hand, someone who hates Apple and borrowed an iPhone and wants to badmouth it, that person will instinctively end up holding it so that reception goes worse.