A change in the wording of Apple's developer agreement in iPhone 4.0 appears to block all efforts by third party platform vendors (including Adobe's Flash and Microsoft's Silverlight) to shim or adapt their code to work as a native iPhone app. Rather than being a competitive blow directed at Flash however, it appears the real motivation is to support sophisticated new multitasking features in the new operating system.

Apple's prohibition of Flash-built apps in iPhone 4.0 related to multitasking