If you are a Burton Group subscriber, you might be aware that Burton is holding a telebriefing panel today on the topic of "iPhone for the Enterprise", which should be good. It sounds like a bit of a REST/SOA point-counterpoint with some panelists stumping for the iPhone and others chopping it down.
I have not yet experience the iPhone (but will next week at Office 2.0), so don't have an informed opinion. Everything I hear sounds like it has a rich browsing experience, and also that Apple is putting forth a good effort to build a development ecosystem around the platform. So who knows, maybe it could happen.
I still think the biggest hurdle at large companies is the perception that the iPhone is just a must-have consumer device. Of course, you can play music and video on many smartphones, but this is where Apple's propensity to do it too much better than everyone else backfires. Do you just want to watch DVDs, or are you getting some work done?
The killer app for the iPhone, against Windows Mobile at least, is stability. If Apple can nail the stability game, go enterprisey when it comes to device management, and get a development ecosystem going, who knows...