Apple says more than 100,000 developers have downloaded the beta iPhone Software Development Kit (SDK) since its release on 6 March.
The iPhone SDK provides developers with the same set of application programming interfaces and tools that Apple uses to create its own native applications for iPhone and the iPod touch.
The SDK is designed to rapidly build up a developer community around the iPhone and help Apple offer a burgeoning array of new apps to iPhone users.
Apple has also previewed the new App Store, a way for developers to wirelessly deliver their applications to every iPhone and iPod touch user.
Developers set the price for their applications and retain 70% of all sales. The system can also be used to distribute freeware.