In February I'll officially run out of reasons to not buy an iPhone. Direct from the horses mouth:
Let me just say it: We want native third party applications on the iPhone, and we plan to have an SDK in developers’ hands in February. We are excited about creating a vibrant third party developer community around the iPhone and enabling hundreds of new applications for our users. With our revolutionary multi-touch interface, powerful hardware and advanced software architecture, we believe we have created the best mobile platform ever for developers.Thanks, Apple.
P.S.: The SDK will also allow developers to create applications for iPod touch.