okay, this ones a bit sticky... okay, when you're at one or more bars you have a "coherant" signal ("x" amount of power from the tower is being read by the phone) Now that signal, low or perfect, may still get garbled by enviromental factors (trees, buildings, how you hold/wear your phone, the "lay of the land.")

visual: imagine you're in a darkroom. the only light in there is blocked, behind a wall or something. now it's really bright, and you can see the effect (strength) of the light, but not well enough to see what it is or use it foranything.

now then, a small penlight (lo signal)no where near as strong is not being blocked by anything you can see quite sharply.

it's not so much the strength as it is the quality of the signal.
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just remember that each manufacturer has it set up to read the signal and give you a strenght meter, these are not always accurate, i have had phones with 0-1 bars and make perfectly clear calls %100 of the time at my house(8000-8100) My 710 and lg 5200 would say 2-3 bars and drop calls on me or incoming calls would not come in? I now have a razr, it says i have 2 bars at my house but will still drop a call every now and then, but my 8100 that was at 0-1 bars never dropped on me, so i don't really pay much attention to the bars, as long as i have some sort of signal i am good, like getting crystal clear calls on my 8100 when it had no signal at all. I have never noticed a difference in call quality as well, at my house with poor signal or at...
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