The firm estimates that Apple shipped 17.7 million iPhones of all kinds to U.S. buyers in the October to December period, meaning it accounted for one in three new phones.
Samsung Electronics of Korea was close behind, shipping 16.8 million phones, including non-smart ones. Samsung has been the largest seller of phones to the U.S. market since 2008, Strategy Analytics said.
NPD Group, another research firm, found that Samsung phones still outsold the iPhone in the quarter, by 31 percent to 29 percent. It tracks retails sales while Strategy Analytics tracks shipments, so the numbers are not directly comparable.
Worldwide, it's clear that Samsung is still the biggest phone vendor with 23 percent of the market, according to a third research firm, IDC. Apple is number three, with 9.9 percent of the market. In between sits Nokia with 17.9 percent.
Samsung beats Apple globally even when only smartphones are considered. It shipped 63.7 million units worldwide versus Apple's 47.8 million.
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.