If you're a fan of the iPhone OS 4.0 right now, and you've tied to the developer program for Apple's mobile devices, then you can go ahead and have your say with the new mobile Operating System. iPhone OS 4.0 SDK is available right now for developers. This is the first of the Betas, so be sure to keep that in mind. And, as always, Apple suggests that you don't put this on your own, personal device, and keep it on your testing devices, because it is Beta, and bugs do happen.
If you're interested, then head over to Apple's developer portal and start the download. If you're a developer planning to develop for iPhone OS 4.0, let us know in the comments, and be sure to tell us what you're going to develop. A game, the next big application? We're interested in hearing from you!