From Engadget:
Speaker / earpiece
We've never had a particular problem with the speaker or earpiece on previous iPhones (well, the speakerphone has never been loud enough for our taste), but it's obvious that Apple has done some work on getting both call quality and speakerphone quality up. Beyond making the phone considerably and consistently louder in both places, the clarity of the iPhone 4 is noticeably improved from the previous generation. If you read our review, then you know that we thought Motorola's original Droid had some of the best sounding components we've heard on a phone, and the new iPhone definitely gives them a run for the money. The first time we took a call on the device we were walking down New York's extremely noisy Fifth Avenue, and right away it was obvious that the secondary, noise-canceling mic was doing some heavy lifting, at least on the other end of the line. Even though sirens were wailing behind us and we were surrounded by chatty shoppers, it was easy to hear our party on the other end, and they could hear us perfectly (unless we were lied to). There's clearly a difference between the sound in the earpiece on the new phone versus the 3GS, and it ranks highly against newer competition like the EVO. As far as the speakerphone goes, it gets loud without distorting or producing cutting midrange, a problem we've noticed on quite a few recent phones. We'd liken the iPhone 4 in quality to something along the lines of the BlackBerry Bold -- a bearable tone even when it gets hot.
