Well I don't know the legitimacy of Mac Beep's claim, but I did go to the store because I was fed up with it not getting/keeping service, my face hanging up on calls, dropped calls, etc. Of course the Apple store rep, at two different locations, said I was probably in a bad reception area...yada..yada...and never admitted to any issues with the phone and where shocked that I had them.
Nevertheless I demanded a replacement after the 14 year old at the genius bar told me to set my phone up as new and it would fix the problems. I didn't buy that argument.
They gave me a new phone and I have to say that I have not been below five bars yet and I've even tried the "death grip" that caused my old iphone 4 to lose service. It seems to be fine, as of now, and hopefully they did secretly fix something. But I'm still skeptical and will see if the new iphone 4 I have will continue to be way better than my old one.