During the iPhone 5 launch event, Apple announced 435 million iTunes accounts (with credit card numbers) with one click shopping.
The account total is updated occasionally by Apple and the history of these updates is shown below:
Measuring the growth in accounts shows steady acceleration.
The current rate is approximately 12 million new accounts per month.
The growth in iTunes accounts mirrors the growth in iOS usage as shown the following chart:
The alignment between the circles and the red line should offer an alternative method of projecting the platform’s growth.
Projecting the growth forward would imply one billion accounts in another two years. As iPhone and iPads growth increasingly converges with iTunes (of which there are 400 million units sold), the same time frame could apply to iOS cumulative sales.
This is not a very precise forecast, but late 2014 to early 2015 could see one iOS billion units sold.