Wow, how insane. The anti-MS RDF is strong here.
Every single person who said, "IMAP4 is e-mail, not calendar" misses the point. You have no idea at all how real enterprise calendaring works. Notes, Groupwise, Exchange - all use e-mail messages and stores to handle calendar messages and information. Either you know that, or you're unqualified to talk to this subject. Go away.
Every person who says "CalDAV", go away. Exchange was there first. It's been doing shared calendaring for A DECADE. Just because a few whiny people don't like the way it does it, doesn't mean Microsoft has any reason to care. The only company of any size and any relevance at all who does care in fact is Apple. (Don't believe me? Too bad. Your belief does not change reality.)
Every person saying, "Security doesn't belong here," go away. Maybe you never have anything in your internal corporate e-mail that you can't share, or maybe you're unemployed. In the former case, you're lying or don't do anything in your company, and in the latter case, good luck with your purchase of a phone with a $2,000 TCO (including data plan for 2 year contract).
Every single BlackBerry user in the world - and there are more of them than there are iPhone owners, and more of them then ever will be iPhone owners, by many times over - know that basic e-mail over IMAP is not enough. E-mail is part of enterprise groupware - pretending it's "just e-mail" misses reality.
So, it's simple - can the iPhone access the GAL? No! (And don't claim that it's because there's no LDAP in an Exchange implementation or that it doesn't work - it's been there for over a decade, and plenty of other products work just fine with it.) Can the iPhone access my calendar OTA, like other products including non-Microsoft products? No! These are features that it was on Apple to get right. It's not up to Microsoft to change their functionality to make Apple's godawful crapfest of a mail/calendar solution work. Apple is the newcomer here. It's arrogant and moronic to blame Microsoft for Apple's inability to do what a large number of other phone suppliers can do. Apple has failed to do what they needed to do.
If you have an iPhone, and don't care about calendaring or a corporate address book or deleting more than one message at a time (!!), then great, I'm very happy for you. Enjoy web browsing on the EDGE network. Enjoy delaing with spam one...message...at...a...time. Enjoy using your own little calendar that no one else can see. Enjoy adding your addresses one at a time for all of your customers, friends, clients, whatever.
I meanwhile have work to do and a life to live, and the iPhone doesn't help with either of those.