Comment by rgovostes

Suppose you always want to be running the latest iOS release, but you want to replace your phone as infrequently as possible. You would "only" have to have purchased 4 iPhones since 2007:

    | Model     | Launch date        | Obsoleted by | Price 
    |-----------|--------------------|--------------|------
    | iPhone    | June 29, 2007      | iOS 4        | $399 (*price cut)
    | iPhone 4  | June 24, 2010      | iOS 8        | $599
    | iPhone 6  | September 19, 2014 | iOS 13       | $649
    | iPhone 11 | September 13, 2019 | -            | $699

Adjusted for inflation, the total for these phones is $3,287 excluding carrier contracts. Assuming the iPhone 11 will be obsoleted by iOS 27 in September 2026, this costs you about $14.29/mo.