Apple's iPhones have never been top-quality phones for voice calling. Blame the networks, blame the radios or blame whatever else you want -- voice calls were almost never a good experience. The iPhone 4S finally starts to break that mold.
In terms of radio performance, speed and call quality, I'm impressed. I have more service in more places, fewer dropped calls (it's about on par with a phone like a BlackBerry 9700, which runs very well on AT&T's network) and better call quality.
What changed? Apple's new antenna system is surely a part of it, as is the updated software on the device, but I think we have to give some credit to the Qualcomm radio that Apple has finally migrated to. Qualcomm is known for making class-topping chips, and that's a welcome change.
