Google has just made their Contact and Calendar synchronization available for Windows Mobile and iPhone phones. This is pretty cool, as it removes the need of using a third party company like NuevaSync or Apple's MobileMe.
I was able to set this up for my account on our Google Apps hosted domain. I got contacts synchronized with my iPhone and one of my calendars. The problem is that I was only able to sync my main calendar. It looks like I should be able to got to http://m.google.com/sync from my iPhone and select which calendars I would want to sync. But that site only accepts main Google account, and not Google Apps accounts.