What operating system does the iPhone use? Can it run MacOS X applications like Skype and Photoshop?

At the MacWorld Expo keynote address on January 9, 2007, as documented by the Engadget blog, Steve Jobs said:

iPhone runs OS X! Why would we want to run such a sophisticated OS on a mobile device? It's got everything we need. Multitasking, networking, power management, security, video, graphics, audio, core animation. . . It let us create desktop class applications and networking, not the crippled stuff you find on most phones, these are real desktop applications.

Not surprisingly, given that Steve Jobs said the iPhone "runs OS X" and "these are real desktop applications", many immediately thought that the iPhone was able to run MacOS X desktop applications like Skype and Photoshop. However, the rather sparse original iPhone technical specifications page on the Apple website noted that the iPhone does in fact run "OS X" as Jobs proclaimed during the keynote, but it does not run MacOS X.

Presumably, the iPhone runs a scaled down version of MacOS X optimized for a handheld device -- although Steve Jobs is insistent that it runs "real OS X" (Specifically, crashlogs indicate that the original iPhone ran "OS X 1.0" build number 1A543a.) -- but no iPhone models can run MacOS X applications regardless. Those with reasonable expectations of the performance limitations of a handheld device likely were not disappointed by this fact.

In the original iPhone Q&A published on February 5, 2007, EveryiPod.com noted:

However, many likely are disappointed that Apple is not openly allowing third parties to develop true applications for the iPhone.

Regarding Skype in particular, in an interview with Steve Jobs, the New York Times reports that:

Apple had "not decided" whether to enable a voice-over-Internet service like Skype -- a potentially divisive issue for Cingular, the exclusive carrier for the iPhone, because it could come at the expense of cellular voice revenue.

Without an open third-party developers program, those hoping for a version of Skype compatible with the iPhone probably should not hold their breath. Apple is unlikely to develop a program in-house that is compatible with Skype or hire Skype to create a version of their product compatible with the iPhone.

Thankfully on October 17, 2007, Apple reversed the foolish decision to not allow third-party development and promised an official SDK in February 2008. The SDK was released on March 6, 2008, and developers immediately began working on applications.

On March 3, 2008, Apple stated that the company would allow the development of VOIP software that uses wi-fi (it would not allow VOIP software to use the cellular network) and ever sense that time the masses had been eagerly awaiting a version of Skype for the iPhone. On March 26, 2009, GigaOM was the first to break the news that Skype for the iPhone was forthcoming, and sure enough, on March 31, 2009, it was officially released to cheers across the Internet.

Skype for the iPhone is free, so one has little to lose by downloading it and trying it out, but iLounge has provided a review that may be of interest. Please note that Skype will run over wi-fi networks, but not over the 3G network provided by telephone companies. Jailbreaking the iPhone -- to run "unofficial" software -- does make it possible to run Skype over the 3G network as well as wi-fi, but the company is combating its use over 3G likely at the request of the mobile carriers.

Nevertheless, fans of Skype should be thrilled that the option of officially making Skype calls on the iPhone using wi-fi finally has become possible.

Can the iPhone run MacOS X or iPod games?

No. The iPhone cannot run any MacOS X applications, including games. It also cannot run applications written for the iPod. However, after opening the device to third-party development, the floodgates opened and a huge variety of games have subsequently been written for the iPhone and iPod touch.