What interests me much more is the by-model breakdown of sales according to NPD. There are currently three iPhone models available — iPhone 4S ($199), iPhone 4 ($99), and iPhone 3GS (free) — and they occupy the top three slots in that order. This may not be an entirely new phenomenon, particularly not for Apple products, but I still find it remarkable. It contradicts what most people keep insisting is conventional wisdom: that cheap and/or free models will always steal volume from premium models. Despite price and variety pressure from various Android models, and even pricing pressure from other iPhone models running the same exact software, the iPhone 4S was still the top-selling smartphone in the United States (according to NPD, at least). And this report is only for October and November — it doesn’t include Christmas.