Apple published an iPhone Human Interface Guideline document.
This document introduces you to the iPhone environment and how it shapes the user experience of iPhone content. Then, it explains how to design a superlative user interface for your web content so it displays and works well on iPhone. It does this by first examining different types of iPhone content and exploring how you can decide which type to create. It then discusses how to apply user interface design principles to iPhone content, and finally provides numerous metrics and guidelines to help you handle specific design issues. For the implementation details and guidance you need to write the code for your iPhone product, see the See Also section below.
Ars notes the suggestive wording that "Currently, developers create web applications for iPhone, not native applications." Regardless, it seems unlikely that this simple wording necessarily reflects any future corporate policy.