I can say within a degree or two of absolute certainty that it will not happen.

1. The iPhone hardware would buckle under many Flash applications.

2. Many Flash applications require a keyboard and mouse to work correctly. When does Safari know to display the keyboard (it can’t be all the time, it takes up half the screen)? What, do we have a virtual mouse? How can we resize the application (it currently isn’t possible without breaking them)? Many Flash applications take advantage of mouse hovers to trigger interface elements, but on the iPhone, you’re either touching the screen or you aren’t. Could Flash applications have some sort of alternative interface for the iPhone that properly fits the screen? So should all Flash developers make two interfaces? It’s a total mess.

3. Apple want to control the mobile video space with Quicktime, not Flash.

4. You cannot write plugins for the iPhone, only individual applications. Only Apple could integrate Flash with Safari. Not even Adobe can do this without negotiating with Apple first; and I can’t think of a reason why Apple would say yes.

Most likely it will never be available, or with some restrictions. Flash would directly compete for developer attention with Apple’s own set of native iPhone development frameworks (Cocoa Touch, OpenGL, and the like). For videos, the YouTube app has Apple’s blessing. And we know how great AppStore games can be. So my answer is no. I do not expect Flash to ever make a true debut on the iPhone platform.