Ars Technica puts font to screen explaining how, even after the jump to version 10.5 Snow Leopard (and several updates), Apple's own Mac OS X Server still fails to integrate push notification and other compatibility for the iPhone:
The iPhone's e-mail, contact, and calendar features integrate poorly into a Mac OS X Server environment, and even after Snow Leopard Server's (SLS) release, they continue to lack instant push delivery capabilities for e-mail, contacts, and calendars to an iPhone from a Mac server. Irony of ironies, the iPhone works better in a Microsoft Exchange world than with Apple’s own server.
Mind boggling. Read the whole article for the technical details and if you're Apple, let's get that fixed, shall we?