The article mentions Apple has 1.2 billion active users. They need 0.014% of those to buy one to hit that number.
The bigger question, also mentioned in the article, is how many of those preorders are scalpers.
The bigger question, also mentioned in the article, is how many of those preorders are scalpers.
More seriously I found 150 million active iPhones in the USA, which would make it roughly 0.12%, or we can use 40% of revenue to scale our original guess (since presumably the US contains a large proportion of those 1.2 billion who would purchase a $3500 device) and get to 0.035%.