How Will iPhone Apps Be Implemented?

John Gruber explores what Steve Jobs could have meant with regard to his announcement earlier this week that Apple would be releasing a development kit for the iPhone:

We now know two new things: (1) that there will be native third party applications on the iPhone; and (2) that the SDK is scheduled for February. That leaves a long list of questions.

Specific comparisons are made to the Danger Hiptop/Sidekick development model which, 9to5mac had suggested Apple was exploring.