This is the best, most in-depth look at everything Apple went through to deliver the iPhone.
Why Apple Can't Just 'Innovate' A New Product Every Other Year - Business Insider:
"Here's an excerpt that sums up what Apple faced when it built the iPhone:
Many executives and engineers, riding high from their success with the iPod, assumed a phone would be like building a small Macintosh. Instead, Apple designed and built not one but three different early versions of the iPhone in 2005 and 2006. One person who worked on the project thinks Apple then made six fully working prototypes of the device it ultimately sold — each with its own set of hardware, software and design tweaks. Some on the team ended up so burned out that they left the company shortly after the first phone hit store shelves. “It was like the first moon mission,” says Tony Fadell, a key executive on the project. (He started his own company, Nest, in 2010.) “I’m used to a certain level of unknowns in a project, but there were so many new things here that it was just staggering.”"
