iPhone model number

Joe Maring / Digital Trends Since its landmark introduction in 2007, Apple has released 42 iPhone models, and with at least four new ones introduced every fall, the company is showing no signs of slowing down. In all that time, Apple has made relatively few significant design changes. The company tends to stick with established designs for three or four years before changing things up, which can sometimes make it difficult to tell which iPhone model you have —  especially if you’re getting a secondhand iPhone (with…