That might sound alarming considering Apple launched the iPhone 8 and iPhone 8 Plus in Q3, but the debuts came at the end of the quarter in late September. Still, Canalys said Apple shipped 13 million iPhone 7 units and 11.9 million iPhone 8 and iPhone 8 Plus devices during the quarter.

By comparison, the iPhone 7 and iPhone 7 Plus hit 14 million in unit sales during the third quarter of 2016, suggesting that demand for the iPhone 8 was muted in comparison and that consumers found cost savings with Apple's year-old devices. Perhaps folks were waiting for the iPhone X, which launched this quarter, too. Canalys said this is key to Apple's strategy of maintaining market share and offering several price points for consumers, ranging from the affordable iPhone SE and iPhone 6s up to the top-tier iPhone X.

Apple CEO Tim Cook has said that demand for the iPhone X is "off the charts."

The iPhone 6s was the second most popular single smartphone model during the quarter with 7.9 million unit sales, trailed by the Samsung J2, the Oppo A57 and the Oppo R11. The latter three aren't sold widely in the U.S. but are popular in China and emerging smartphone markets.

Apple's iPhone 8 and iPhone 8 Plus were responsible for 5.4 million and 6.3 million units, respectively, according to Canalys, showing that the larger iPhone 8 Plus was the preferred model.