A research firm says that Samsung's Galaxy S3 overtook Apple's iPhone 4S as the world's best-selling smartphone for the first time in the third quarter.

Boston-based Strategy Analytics said Thursday that the S3 shipped 18 million units in the third quarter of this year. Apple Inc.'s iPhone 4S, meanwhile, shipped 16.2 million units, as many people likely held off to buy its successor. Apple launched the 5 on Sept. 21.

Strategy Analytics' executive director, Neil Mawston, says the Galaxy's top position is likely to be short-lived. The sold an estimated 6 million units in the third quarter, which ended on Sept. 30.

Apple shares continued their recent decline in morning trading, falling $8.62, less than 2 percent, to $549.38. The stock was over $700 two months ago.