The secret Application SDK key which keeps the iPhone locked has been leaked onto the Web. According to Tauw.com, the key has appeared at several places on the Web.

iPhone applications must be properly signed for iTunes to process them and for the iPhone to load them. So, the publication of the key indicates that hackers are closer to creating compliant IPA application bundles for home-brew iTunes distribution.

It means that software that does not need Apple's blessing can be used on the iPhone and still use iTunes. That is, unless Apple tries to change its SDK key.

More here.