No one had ever put a multitouch screen in a mainstream consumer product before, either. Capacitive touch technology — a “touch” by either a finger or other conductive object completes a circuit — had been around since the 1960s. Capacitive multitouch, in which two or more fingers can be used and independently recognized, was vastly more complicated. Research into it began in the mid-1980s. It was well known, though, that to build the touch-screen Apple put on the iPhone and produce it in volume was a challenge few had the money or guts to take on. The next steps — to embed the technology invisibly in a piece of glass, to make it smart enough to display a virtual keyboard with autocorrect and to make it sophisticated enough to reliably manipulate photos or Web pages on that screen — made it hugely expensive even to produce a working prototype. Few production lines had experience manufacturing multitouch screens. The touch-screens in consumer electronics had typically been pressure-sensitive ones that users pushed with a finger or a stylus. (The PalmPilot and its successors like the Palm Treo were popular expressions of this technology.) Even if multitouch iPhone screens had been easy to make, it wasn’t at all clear to Apple’s executive team that the features they enabled, like on-screen keyboards and “tap to zoom,” were enhancements that consumers wanted.

As early as 2003, a handful of Apple engineers had figured out how to put multitouch technology in a tablet. “The story was that Steve wanted a device that he could use to read e-mail while on the toilet — that was the extent of the product spec,” says Joshua Strickon, one of the earliest engineers on that project. “But you couldn’t build a device with enough battery life to take out of the house, and you couldn’t get a chip with enough graphics capability to make it useful. We spent a lot of time trying to figure out just what to do.” Before joining Apple in 2003, Strickon had built a multitouch device for his master’s thesis at M.I.T. But given the lack of consensus at Apple about what to do with the prototypes he and his fellow engineers developed, he says, he left the company in 2004 thinking it wasn’t going to do anything with that technology.

Tim Bucher, one of Apple’s top executives at the time and the company’s biggest multitouch proponent, says part of the problem was that the prototypes they were building used software, OS X, that was designed to be used with a mouse, not a finger. “We were using 10- or 12-inch screens with Mac-mini-like guts . . . and then you would launch these demos that would do the different multitouch gestures. One demo was a keyboard application that would rise from the bottom — very much what ended up shipping in the iPhone two years later. But it wasn’t very pretty. It was very much wires, chewing gum and baling wire.”

Few even thought about making touch-screen technology the centerpiece of a new kind of phone until Jobs started really pushing the idea in mid-2005. “He said: ‘Tony, come over here. Here’s something we’re working on. What do you think? Do you think we could make a phone out of this?’ ” Fadell says, referring to a demo Jobs was playing with. “It was huge. It filled the room. There was a projector mounted on the ceiling, and it would project the Mac screen onto this surface that was maybe three or four feet square. Then you could touch the Mac screen and move things around and draw on it.” Fadell was aware of the touch-screen prototype, but not in great detail, because it was a Mac product, and he ran the iPod division. “So we all sat down and had a serious discussion about it — about what could be done.”

Fadell had strong doubts about shrinking such an enormous prototype so much and then manufacturing it. But he also knew better than to say no to Steve Jobs. He was one of Apple’s superstars, having joined the company in 2001 as a consultant to help build the first iPod, and he didn’t get there by being timid in the face of thorny technological problems. By 2005, with iPod sales exploding, he had become, at 36, arguably the single most important line executive at the company.

“I understood how it could be done,” Fadell says. “But it’s one thing to think that, and another to take a room full of special, one-off gear and make a million phone-size versions of that in a cost-effective, reliable manner.” The to-do list was exhausting just to think about. “You had to go to LCD vendors who knew how to embed technology like this in glass; you had to find time on their line; and then you had to come up with compensation and calibrating algorithms to keep the pixel electronics from generating all kinds of noise in the touch-screen” — which sat on top of the LCD. “It was a whole project just to make the touch-screen device. We tried two or three ways of actually making the touch-screen until we could make one in enough volume that would work.”

Shrinking OS X and building a multitouch screen, while innovative and difficult, were at least within the skills Apple had already mastered as a corporation. No one was better equipped to rethink OS X’s design. Apple knew LCD manufacturers because it put an LCD in every laptop and iPod. Mobile-phone physics was an entirely new field, however, and it took those working on the iPhone into 2006 to realize how little they knew. Apple built testing rooms and equipment to test the iPhone’s antenna. It created models of human heads, with viscous stuff inside to approximate the density of human brains, to help measure the radiation that users might be exposed to from using the phone. One senior executive believes that more than $150 million was spent creating the first iPhone.