Apple has basically doubled its iPhone sales in the last three years, according to estimates from research firm IDC. On its own, that's a considerable achievement. But more than that, it has maintained prices for them, too, in the face of discount competition from various high-quality Android phones. This year it's expected to eke out a small increase in price, too, according to IDC.
What's missing from this chart is the obvious: The effect of iPhone 6. Apple is expected to launch the new big-screen version of its phone in the fall, giving the company a massive 2015 in terms of both units shifted and price level maintainance.