When the iPhone was first announced last June, programmers were excited by the possibilities it presented, but Apple withheld a lot of information about the inner workings of the phone's software. Instead of promoting downloadable applications, Apple encouraged the development of Web-based programs that ran inside the Safari browser. But that limited the programs' capabilities. For instance, they could not take full advantage of the touch screen or the three-axis accelerometer, and they couldn't store data on the phone's flash-memory chip. Some programmers turned to hacking the phone--in essence reverse-engineering instructions that control the hardware--so that they could build their own applications, including virtual guitars. (See "The Next Generation of iPhone Hacks.")
Some of the software that the early iPhone hackers developed, such as the virtual guitar and games that use the accelerometer, illustrates the potential of the SDK. The entrepreneur and iPhone expert Christopher Allen, for instance, envisions writing software that could filter calls or text messages depending on the position of the phone: laying the phone flat on your desk might indicate that you want to accept only work-related calls. (See "The iPhone's Untapped Potential.")
Nonetheless, says Allen, it's still not a complete free-for-all. It's not clear whether programmers will have access to certain layers of information about the phone, such as those that could allow them to build Bluetooth peripherals like keyboards. Allen says that he hasn't yet had a chance to dive deeply into the SDK, but he's not sure whether it will allow for software that lets iPhone users receive data, such as instant messages, while they're placing calls over the cellular network (something that's not possible now).
Already, Apple has enlisted some major companies to develop early applications that will give the public a taste of what the development kit allows. At the press event, AOL unveiled its iPhone-compatible instant-messaging program, and the game company Electronic Arts showed off Spore, a game that uses the accelerometer to control play.
While the SDK is downloadable right now, third-party programs written for the phone won't be available until June, when Apple releases the iPhone 2.0 update. At that time, people will be able to download programs via iTunes, in the same way that they download songs and movies. Allen suspects that, as it has with podcasts, Apple will promote the programs that are the most popular, "which means the quality stuff wins," he says. "That's definitely not what's happening in the cell-phone world right now: quality is not there." Of Apple opening the iPhone, Allen says, "I think this is a pivotal thing."