Steve Jobs made it official Wednesday morning: third-party applications are coming to the iPhone.

Apple's CEO posted another of his open letters to the world Wednesday on Apple's Hot News section of its Web site, confirming reports that a software development kit (SDK) for the iPhone will be released to developers next year. It's coming in Februrary, rather than January as reported, but application developers and iPhone owners will probably be able to wait the extra month.

"We are excited about creating a vibrant third party developer community around the iPhone and enabling hundreds of new applications for our users," Jobs wrote. "It will take until February to release an SDK because 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."

It always made sense for Apple to go down this road, since it was never going to win a hacking war and users clearly want third-party applications on their iPhones and iPod Touches, which will also be opened up by the SDK, Jobs confirmed. I actually thought it would take a little longer for Apple to open its precious iPhone up to developers, but the company probably has become more satisfied in recent months with the stability of the OS X operating system. Apple has always said that the iPhone runs Mac OS X at its core, but in practical terms it's really a new operating system that Apple has put together for the iPhone with common DNA from Mac OS.

Jobs implied that the first iPhone SDK would be a step past what Nokia is doing with its developers. Nokia has a huge developer community that creates applications for both Java and Symbian-based phones, and Jobs said those applications are required to have a digital signature that verifies the application has passed certain tests, and that makes sense given the growing concerns about smartphone security.

"While this makes such a phone less than 'totally open,' we believe it is a step in the right direction," he wrote, hinting that Apple would somehow make it possible for almost any developer to add trusted applications to the iPhone using the SDK.

We'll have to see how Apple decides to strike a balance between openness and security, but it's good to see the company acknowledge that there are more options for keeping the iPhone secure than just limiting developers to Web applications.