Apple has said it will open the iPhone and iPod Touch to outside developers, reversing its earlier strategy of keeping the devices all to itself.

In an open letter posted on Apple's website, CEO Steve Jobs said that a software developer's kit (SDK) will be released in February. "Let me just say it: We want native third-party applications on the iPhone," Jobs said.

"We are excited about creating a vibrant third-party developer community around the iPhone and enabling hundreds of new applications for our users," he added.

The announcement was a 180-degree turn from Apple's original position, which had iPhone applications off limits to all but the company's own developers and had outside apps restricted to web-based programs that ran in the iPhone's Safari browser.

Until yesterday, Jobs had defended that strategy security grounds, saying that the closed iPhone was necessary to insure the device's security and reliability. Several times, Jobs had expressed worries about third-party applications crashing the iPhone. "The more [third-party applications] you add, the more your phone crashes," Jobs said a month before the iPhone's launch. "No one's perfect, and we'd sure like our phone not to crash once a day."

He has now tacitly acknowledged the earlier stance in explaining why the SDK won't ship until February. "We're trying to do two diametrically opposed things at once - provide an advanced and open platform to developers while at the same time protect iPhone users from viruses, malware, privacy attacks, etc. This is no easy task."

Even though the announcement was a turnabout, it was not unexpected. In late May, Jobs had hinted that the iPhone would be opened eventually. "If you can just be a little more patient with us, I think everyone can get what they want," he said when talking about third-party applications.

"I can't say I'm surprised," said Van Baker, an analyst at Gartner. "It was inevitable, really."

Apple didn't roll out an SDK immediately because it needed to gauge the system's stability and security before opening the device to application developers, Baker added. Another factor in the decision, Baker said, was that Apple figured out the back and forth between the company and programmers modifying the iPhone was not only futile, but also bad business.

"It realised that this ongoing battle is not a good thing," Baker said. "People found that they really used and enjoyed [the unsanctioned modifications and programs], and for Apple to continue to break them was not in their best interest."

Late last month, for instance, the 1.1.1 update to the iPhone's firmware not only "bricked" phones that had been hacked to work with mobile carriers other than AT&T - "unlocked," in the company's parlance - but also broke or disabled or deleted third-party applications installed on the device. That move was seen by many as the logical result of what Jobs himself called a "cat-and-mouse game" between Apple and hackers who wanted to modify their phones. "People will try to break in, and it's our job to stop them breaking in."

Missing from the announcement were details of the SDK and how Apple would secure the iPhone when others were allowed to code native applications. Jobs however, gave a clue or two. "Nokia, for example, is not allowing any applications to be loaded onto some of their newest phones unless they have a digital signature that can be traced back to a known developer," he said. "While this makes such a phone less than 'totally open,' we believe it is a step in the right direction."

But even as he said the iPhone - and by extension, the iPod Touch - would be opened, Jobs continued to voice concerns about risks to mobile devices in general and to the iPhone specifically. "As our phones become more powerful, malicious programs will become more dangerous. And since the iPhone is the most advanced phone ever, it will be a highly visible target," Jobs said.

Coincidentally, yesterday noted hacker HD Moore released attack code that exploits a critical iPhone vulnerability.

But the news that an SDK is coming doesn't mean that everything is suddenly legal. Apple will continue to fight unlocking, Baker said. "To do otherwise would violate the agreement they have with AT&T," he said.