When Steve Jobs unveiled the iPhone in 2007, he set an ambitious goal: 10 million iPhones sold in 2008, the first full year the phone would be available.
Pundits were skeptical. They pointed out that Apple had no experience selling phones, and that most phones being sold then were cheaper "feature phones," not smartphones. Apple did meet its goal, selling more than 13 million iPhones in calendar 2008.
Today, the iPhone is a much, much more popular product. How much more popular? Apple's new iPhone 6 line, which went on sale on Friday, has already sold 10 million units.
This was made possible by a bigger and more sophisticated Apple supply chain, which was able to pump out millions of units in time for the big launch. It was aided by millions of pre-orders, which allowed Apple to ship many phones directly to customers' houses. And fundamentally, it reflects the fact that tens of millions of customers love their iPhones.
Update: I originally reported that Apple sold 11 million iPhones in 2008, but this was the figure for Apple's fiscal year. I've updated the story to reflect calendar year 2008 sales of more than 13 million iPhones.