Research firm: Apple now biggest US phone seller

IPhones are more expensive than most Samsung smartphones. They're well within reach for U.S. buyers, but not for buyers in the developing world, where cheaper phones running Google Inc.'s Android operating system dominate.

In the U.S., iPhone sales are usually very strong in the first few months after a new model is released. They then taper off. That means Samsung could regain the phone crown as early as this quarter, as measured by Strategy Analytics.

NPD said the iPhone 5 was the single most popular phone in the U.S. in the holiday quarter. The Samsung Galaxy S III was No. 2, followed by the older iPhone models, the 4S and 4.