What you can't do with the iPhone – out of the box, anyhow – is to get the BlackBerry's push-based approach to email, where the mail server sends messages to the device, rather than requiring the device to query the server to gain access to new messages. This push-based approach makes it harder for someone to spoof the email server.
To push email to an iPhone (or most other mobile devices), you need a mobile server such as those from Visto and Synchonica; these integrate with your Exchange or Domino server.
The iPhone also doesn't support Microsoft's Direct-Push approach (aka ActiveSync on Windows Mobile and Palm OS devices), which leaves the connection between the OWA (Outlook Web Access) server's mail port and the mobile device open so that new messages are instantly visible. The iPhone does use OWA as its connection to Exchange, just as Microsoft's Entourage email client does for the Mac OS.
Instead, you'll have to live with the iPhone's periodic mail checks; 15 minutes is the shortest period, although you can easily find SSH hacks on the Web to reduce that. Rumours have been flying for months that Apple has licensed ActiveSync from Microsoft; maybe we'll find out on Thursday whether those rumours are true.
Accessing calendars and other shared data
The biggest issue Exchange and Notes businesses will face in business-enabling the iPhone is providing access to calendars, address books, and other PIM data beyond email.
Calendars and contacts can be synchronised between Exchange and the iPhone, but this must be done through iTunes, meaning you will need a PC or Mac to act as an intermediary.
For Windows (XP or Vista) businesses tapping Outlook 2003 or 2007, synching is straightforward through iTunes. Connect the iPhone to your intermediary PC and select it in iTunes' devices list. Open the iTunes device info pane and choose the calendars and contact sources you want to sync. If you have problems, consult Apple's common fixes.
On the Mac, use the built-in iCal and Address Book software as the waystation, and then configure Entourage to sync with them (using the Sync Services pane of the Preferences dialog box). In iCal, you must create and use a calendar called Entourage for any entries you want synched to Exchange. (And Exchange calendar items will be placed in iCal in the Entourage calendar as well.) Then, with your iPhone physically connected and selected in iTunes' Devices list, open the Info pane to choose the calendars and contact sources to be synced. All three programs – Entourage, iCal, and iTunes – must be set up properly for this ménage à trois to work.
A tip for Mac users: in Entourage's preferences, choose whether to sync your server's calendar or your local calendar. If you change this setting, it's very likely that your calendar will stop synching. It turns out the issue is in iCal. You'll see multiple Entourage calendars listed (one for each time you changed the setting in Entourage). Delete all but the "real" Entourage calendar (you can right-click on a calendar and choose Delete from the contextual menu).