Yankee Group explains: it's not that the service is great, it's more that the phone is awesome. Customers really love their iPhones, and so even when the reception isn't very good, the overall experience scores high. AT&T says it's just a perception problem: "There's a gap between what people hear about us and what their experience is with us. We think that gap is beginning to close," according to a spokesman.
I'll say this: I carried my iPhone all over San Diego at Comic-Con last week, and the reception I got was just plain terrible. My net connection barely worked, calls were dropped, and I couldn't check email even when I needed to. But I'll admit that the AT&T problems exist in a strange place -- not only does the iPhone's otherwise shining example of user experience helping to outweigh AT&T's problems, but customers' high expectations for the iPhone probably have something to do with all of the complaining as well.