In his iPhone review, Walt Mossberg mentions that the device will work with Microsoft Exchange, allowing access to one of the most widespread corporate email systems. One of the many pre-launch arguments against the iPhone was that it is not for business users.
To function with Exchange, Apple would presumably have to license ActiveSync from Microsoft. If true, it marks a significant turn for Apple, and means that it is taking a serious crack at the business market. Of course, like the iPod, it will still be dangerous in the workplace.