Ars Technica writes that a source at Apple has told them that Apple is developing solutions to expand the power and capabilities of the current web-based SDK "but there are currently no plans to offer a "true" iPhone SDK that would allow developers to create native apps."
Apple is going to offer several enhancements to the current SDK instead, for example allowing web pages to be accessed while offline, effectively making the iPhone capable of serving up applications while not connected to the internet.
Also Apple is planning to implement the ability to add home buttons as well as more local phone functionalities from applications via JavaScript.
Apple is currently aiming for an unspecified "January" deadline on these updates, with a most likely announcement date of Macworld 2008.