According to this article on Electronista Apple has started delivering iPhone SDK’s to some selected partners.
It seems like the SDK is not a full SDK, but a way to produce applications in a contained programming environment. Sounds like Apple did not get it and the fact that lots of developers wanted to hack and build their own fully native apps was not enough of a signal.
Also, can you imagine how many developers you could bring to the Mac once they have developed something for the trendy iPhone?
It’s a missed opportunity to me. The whole “signed application” process is a bit of a pain (Symbian developers can probably tell you something about this), but reasonable (especially if you want to create a “walled garden 2.0” in iTunes), but not allowing developers to create at all is a misake.