As the hour of the iPhone SDK closes in, two schools of rumour predominate. The first claims Apple will only introduce a beta version of the iPhone SDK this evening, with the final version set to debut in June, around the time of the Worldwide Developer's Conference.

The second - and latest - rumour claims Apple will require iPhone application development to be conducted using Mac OS X 10.5 Leopard. That's because the development tools will be added as an extension to the company's existing XCode development suite.

That makes sense because XCode is a Mac OS X-native application development solution, and the iPhone is itself OS X-based.

Check back this evening when Macworld UK will offer full run-down of Apple's announcements tonight.