To mark the iPhone's 5 year anniversary, comScore has released a chart of mobile use by iPhone type:
The most striking thing about the chart, to me, is how steady the width of the bands remains through time. There is a perception that a small but dedicated group of iPhone owners upgrade their hardware with each new release, inflating the number of devices sold (this idea is preposterous in the face of the number of units Apple ships each quarter, but it persists nonetheless). Here, the evidence shows that the release of a new phone draws new buyers rather than cannibalizing old ones. Each strata grows only when its respective device is on sale, which makes sense -- note that both the iPhones 3GS and 4 remained available as low-cost alternatives to the subsequent flagship.