This is quite a typical question but i have seen wildly different approaches on that one. How would you rate my approach? I tried to be straightforward
1.) assume 300 Mio people in the US - 8/10 will have a smartphone, 2/10 will have either no phone or now smartphone -> pop. with smartphone = 240 M. ; pop without = 60 M
2) staying on the branch of people who own a smartphone for now - lets estimate an average replacement rate of 3 years. This would mean that 80 M phones will be replaced in each given year
3) of that 80 M. phone buyers, let's assume three income levels a) low b) medium c) high . I would say 30% is in the lower income bucket, 50% in the medium income and 20% in the high income
4) for the low income bucket I would assume that only 1 out of 10 persons is able to afford a (new) iphone = 2.4 M ; for the medium income person I assume that 4/10 person would buy an iphone, mentioning here that competitors such as samsung will take a large share of the market s well = 16 M. ; finally, for the high income bucket I would actually estimate that 7 out of 10 people buy an Iphone - that is reasonable by my assumption, and would equal another 10.2 M. iphones
5) lets look at the second branch: I would assume that first time smartphone buyers will not be inclined to buy a high end phone such as an iphone, say 1/10 there which would total another 6 Mio Iphone
Overall this would lead to approximately 29 Million Iphones bought in the US each year.