So Apple has announced that the iPhone will be getting an SDK in February. There’s not direct link to the news so if you haven’t read it yet (where have you been?) check http://www.apple.com/hotnews/ and look around.
There are still lots of unanswered questions though. John Gruber goes over some of the remaining questions. It seems clear that Apple will still want to control what apps your are allowed to install on your iPhone and will void your warranty if you try to do an end run around their system.
I haven’t bought an iPhone yet, but that seems like it is only a matter of time. My 2 year contract with Verizon ends in March, which would make switching less painful.