Since OS 3.x, you could sync Exchange calendars and meetings (that's what I used mine for mostly) as long as you allow that person to get their mail via Exchange.

Remotely, we set up a forward facing port for our Exchange server that would allow off-site sync as well.

From what I've seen, iPhone OS 4.0 Beta 2 didn't add anything there.

I wonder if PR1.2 added provisioning though... hadn't seen that confirmed yet.