That's the rub. These things (and by this I mean 'smartphones', not just the iPhone) are designed to be pocket computers, with varying degrees of success. The people who buy them want shiny screens, more memory etc, without any concern for basic features like 'how good is it as a phone'. It's the whole cameras and megapixels debacle all over again.
I've lost count of the number of shiny gadgets I've had, only to find post-purchase that it doesn't do something fundemental very well. I've had all-singing-and-dancing phones that don't have sufficient processing power to drive the UI properly; I've had ones that will ring or vibrate, but not at the same time; I've had gadgets that are great so long as you reboot them daily, or have 20 minutes battery life unless you disable half of the features you bought it for; etc etc.
I don't doubt that the iPhone is at least a reasonable "phone," but I'll be surprised if call quality and antenna sensitivity were fairly high on the list of design priorities. The days are gone where you could have a 6310i and get a mobile signal on the surface of the moon. Never had one myself, but -that- is how you make a good phone rather than a marketing-friendly, desireable gadget.