From Seeking Alpha (free reg-wall):

Tim Cook was pleased to announce that in FY2014, Apple sold 250 million iOS devices. That means that since 2007, Apple has sold over 950 million iOS devices in total and is on track to sell it’s billionth iOS device sometime in Q12015. The only other platforms to ever reach the billion milestone are Windows, Facebook, and Android. This is a significant milestone and unlike with Facebook, the billion dollar figure does not suggest the same penetration as Android or iOS, since the latter two act more as an annuity, where consumers purchase upgrades in rather regular cycles.

I remember thinking, when the iPhone was first announced, what an accomplishment it would be if Apple could sell 10 million of them. A billion iOS devices is simply astonishing.

Interesting point about the relative achievements of a billion Facebook accounts versus a billion iOS devices. Certainly fair to say that a billion Facebook accounts is the harder of the two, requiring deeper market penetration. On the other hand, it does say something that Apple has a lot of repeat customers and requires them to survive. With Facebook, if you’ve ever had an account (as long as you don’t delete it), that number counts, even if you no longer use the service.