The iPhone has no doubt been a crazy success since the early days. But how did the iPhone end up being such a success? Speculation, rumors and the lack of a design-first company in the market left Apple wide-open to squeeze into a already crowding market of cell phones and catalyze the smartphone industry into the behemoth that it is today. It took years of research, iteration and trial and error to produce the first iPhones. Apple was prototyping devices in secrecy with fabricators in China as early as 2005 with Foxconn and Pegatron. Looking back, we can see the design lineage and early ideas that were afoot in the company.
Early on, there was a bet that the clickwheel, an invention of the successful iPod could be re-used in the iPhone. Thanks to @DongleBookPro, and (a few others over the years), we have some interesting images of late Acorns OS. Apple installed numerous diagnostic tools on these devices such as fabricator diagnostics, carrier and engineering diagnostic UI. Hap Plain of Cult of Mac put together this video showing just how rudimentary some of these early P-series iPhones worked here:
The rudimentary touch-operated Acorn OS that ran on these prototypes eventually were refined and became the much beloved iOS. For further reading I recommend 9to5mac’s piece on the history behind Acorn OS and how it came to be.