It's still a few months off, but this week Apple and Microsoft announced that Apple has licensed ActiveSync for the iPhone. Exchange Server is the premier messaging system on the market and is widely used by corporations around the world. The iPhone has garnered it's share of publicity and interest so it seems natural that a killer phone would want killer email.
If you head on over to http://www.apple.com/iphone/enterprise/, you'll see Apple is accepting applications into their beta program. Here's the excerpt from their page about Exchange:
Microsoft Exchange ActiveSync support
If your office uses Microsoft Exchange Server 2003 or 2007, iPhone 2.0 software will allow you to wirelessly push company email, calendar events, and contacts over Wi-Fi or EDGE networks to iPhones. With secure push email and over-the-air contacts and calendar features, users will stay up to date wherever they go. And thanks to the iPhone Multi-Touch display, users will find it easier to perform common tasks such as accepting meeting invitations and finding contacts in the company directory or Global Address List (GAL).
IT administrators can securely manage any iPhone that contains confidential company information with remote wipe and enforced security and password policies. These device configuration and remote management capabilities allow IT departments to quickly and seamlessly deploy iPhone throughout their companies.
You should also check out the question and answer section with Microsoft Corporate Vice President, Terry Meyerson at http://www.microsoft.com/Presspass/Features/2008/mar08/03-06EASqa.mspx.
Interesting times indeed...