Speculation on whether Apple is planning to open up the Apple iPhone to third party applications has been running rife over the past few weeks.

We reported a few weeks back that Apple was already working with key developers to bring new applications to the Apple iPhone. Now BusinessWeek says that the firm already has a software development kit (SDK) ready, and that it is likely to be announced in Steve Jobs' keynote speech at the Macworld Expo show next January.

The reason why it's taken Apple so long to release the development kit apparently isn't that the firm has anything against third party developers gagging to get their hands on the Apple iPhone. Rather, that it wanted to wait until the release of Mac OS X 10.5 Leopard, which is now scheduled for release on Friday 26 October.