At the joint Cingular/Apple press conference last week, the press reps made one thing very clear, users will have no access to the internal workings of the device. It will come equipped with a standard set of widgets, that Apple may or may not expand in the future, but there will be NO third party applications available for it. The reason for this is, according to industry insiders, the API for the device hasn't been developed yet. In fact, any API for the Apple iPhone is at least a year away from being handed to developers, so obviously applications are a lot further off.
The iPhone will act as a phone, act as an MP3 player, act as a video player, act as an Internet surfing device (better on its Wi-Fi than the included EDGE wireless data), and will manage contacts, calendar and such, but it will NOT become a replacement PDA or enterprise-class smartphone. There will be no Exchange integration. Access to email we be via Cingular's MEdiaNet portal or over the regular Internet, it will not be pushed from any third party server to the iPhone. There will be NO wireless updating to the included calendar. That will occur only via the USB hard syncing capabilities with the user's home computer.
Apple wouldn't even imply whether or not users would be able to self-load widgets in the future. If you ask me, BlackBerry's will continue to reign supreme as the enterprise smartphone of choice.
The take-home point is this: you won't have to support the Apple iPhone any more than you do the current generation of iPods. So relax, put your feet up, and worry about how much a pain in the ass it is going to be to migrate your enterprise IT organization to Vista instead.