Let's take a different route then. OMG - the 3GS has same problem, always had.
http://www.youtube.com/watch?v=QNSSxxnSweY
I replicated his test on my 3GS perfectly. In the 1+ years of use, I have never noticed it. I'm right handed but hold in my left always. I've had about a dozen dropped calls in that time. When that happens, I physically move, usually about 30 feet, maybe change my grip or go to speaker phone so I can watch the signal meter more carefully and call completes w/o issue. Prior to iPhone 3GS, had various smartphones... I had dropped calls then too - about same rate. Instead of going back to test these or theorize, I'll just say I've learned to live with the occasional drop call and not dive too deep into reasoning why.
What's the difference? Why the sudden craziness? Because it's technically fascinating (if not, then you'd apply a workaround vs. just talking about it). And this doesn't just apply to the iPhone 4. Do you have this issue with the iPhone 3GS, or ANY other phone... WORKAROUNDS are many: return phone, buy case, hold differently, move to better reception, send Steve Jobs an e-mail with another possible solution. What is not a solution is to continually complain on forums. Again: return phone, buy case, hold differently, move to better reception, send Steve Jobs an e-mail with another possible solution, or if you organize - try a class action lawsuit.
The most Apple will do, and should do possibly, offer a discount for the rubber bumper case for those reporting the problem or money back. I doubt they will change the design if it helps with overall reception. And unless enough mass develops (which this sort of conversation is certainly helping to drive), there is no incentive for them to change anything.
I'm not an Apple troll or fanboy, just someone who works with IT organizations all the time on critical and non-critical issues. The amount of resources wasted on the non-critical ones always amazes me. This would have gone the way of the 3GS reception problem if it weren't for the 'critical' nature of the hype.