The iPhone is as much a music player as a phone, so every iPhone comes with a special microphone headset with some external controls in the chord. Many iPhone users (myself included) prefer to talk on the phone via this headset. Using the headset you get better sound quality for both parties, can hear with both ears, can move more freely and be more comfortable and
can use the phone to take notes or check your calendar or look something up on the internet while you talk. So when you talk on an iPhone, the phone might be in your pocket or in your lap or on the desk in front of you or just about anywhere. This presumption that people who are talking on the phone
must be holding the phone by its base against their head is frankly a relic of an earlier time when phones weren't also good music players.
If you're listening to music and receive a call, one squeeze to the headphone chord answers the call, then the music comes back up where it left off when you or the other party hangs up. It's really convenient.
The AT&T network was kind of crappy for a while because they had trouble keeping up with demand. This perception issue only affected people who didn't use headphones and held the phone in a certain way and had unusually poor local signal strength...but even then, it wasn't appreciably worse than the situation those same people would have faced with the prior model, the 3GS.
