Android uses Microsoft Exchange Server. If your company or provider uses it and you have the access needed it can push email and will two way sync calendar and contacts.
My understanding is that stock Android does not support calendar sync via exchange.
Not true. I have used a Droid with my Exchange calendar. It just puts it in the separate exchange calendar app.
The Android Exchange sync on 2.0.1 has another peculiarity. When syncing with Exchange servers prior to 2007, you will not get HTML formatted email. I've seen several explanations that this is a server side issue but I have iPhone users syncing to the same server and they get HTML but Android users do not.