I listened to a Burton Group briefing on whether or not the iPhone is enterprise ready. The briefing started with a slide show that concluded "that while the iPhone will fundamentally influence future smart phones, it isn't enterprise ready."
Bob Blakley, however, had a dissenting opinion that I think makes a lot of sense. There are several reasons for saying the iPhone isn't enterprise-ready: no provision for encrypting resident data, no way to load apps, and no provision for resident data. While you can certainly make a case that encrypting data on the device (even contacts) is necessary for many enterprises, the model that keeps apps and data on the Web--removing the need for these to be remotely managed--is exactly the kind of mobile platform enterprises ought to want.
There are applications you can think of--field technicians in areas with poor connectivity who need access to large amounts of data--but those are probably the exception, not the rule. Most road warriors could use Web-based tools with little loss in productivity. I have been amazed at the richness of some of the iPhone applications that I've seen and it's only been a few months.
Creating Web-based applications and data might not work for every enterprise, but if it works for you, then the iPhone, and it's future copycats, might prove to be a superior platform. Don't make the mistake of thinking that just because the iPhone doesn't work like the last generation of mobile devices that it's not right for your organization. Regardless, the iPhone portends changes for the mobile market and it's worth paying attention to what that means for your enterprise.