Developers have access to wide variety of tools, but all apps ultimately will be sold by Apple

Apple unveiled its long-promised software developer’s kit for the iPhone today and, as expected, announced support for Microsoft Exchange, allowing enterprises to bring the hip and powerful device into their corporate folds for the first time. But Apple CEO Steve Jobs had one surprise. He announced a new version of the iPhone software scheduled for release in June, which could be a prelude to a new version of the iPhone.

Apple released the SDK for public download as well as an iPhone emulator for the Mac that would allow software makers to test their apps out on a program that simulates the iPhone’s interface. The iPhone 2.0 software, however, only went out to a select group of development partners and enterprises as a Beta release, allowing Apple’s partners to get a leg up on development on a real device.

The initiative with the biggest immediate impact, though, is Apple’s licensing of Microsoft’s ActiveSync, which allows the e-mail applications running natively on the iPhone to synch securely to Exchange servers, opening a potentially huge market for the iPhone in the business community.

“We’re excited about creating a vibrant third-party developer community with potentially thousands of native applications for iPhone and iPod touch,” Jobs said in a statement. “iPhone’s enterprise features combined with its revolutionary Multi-Touch user interface and advanced software architecture provide the best user experience and the most advanced software platform ever for a mobile device.”

The big question is how much freedom Apple will give its new developer community. As expected, Apple is limiting all application distribution to an App Store it has linked to iTunes, but Jobs did not lay out a framework for how applications will be authorized for the iPhone or the App Store. Several news reports have cited developers complaining about the limits Apple plans to place on what types of applications can be developed and ultimately what will be approved for distribution and sale. But based on the tools Apple released in the SDK today, it doesn’t appear to be placing many boundaries on the developer community.

Apple has retooled its Cocoa application framework of Mac OS X for the iPhone and its touch-screen interface. It has also provided access to most of the iPhones application programming interfaces (APIs), including all of the iPhone’s touch and gesture controls, location function and multimedia capabilities, on device storage and even the accelerometer, the sensor that determines what orientation the user is holding the device in.

The App Store itself we be added to the firmware of all iPhones when the new OS is released in June, which allows customers to browse and buy particular apps from the iPhone itself or over iTunes for later upload to the device. The seemingly innocuous store, though, has the potential to be one of the most celebrated yet controversial elements of the new developer program. It will provide an easily accessible and—knowing Apple—well designed portal for discovering and purchasing apps analogous to the way music and video is bought on iTunes. But as a central application repository, the App store could function much like a closed carrier portal, not only limiting what applications are available to the user but favoring the applications of Apple’s partners.

Jobs said all developers would be treated equally, however, and that all sales would fall under a 70/30 revenue split favoring the developer. What’s more, he said, Apple will handle hosting and marketing as well as the entire billing process through the iTunes account, and it will distribute developers’ cuts on a monthly basis. As far as Apple’s control over the content, Jobs laid out only a few broad parameters: no porn, no apps that breach others’ privacy, no bandwidth-intensive apps and nothing malicious or illegal. But Jobs did lay out one huge caveat: Apple would also restrict applications “unforeseen.”