With the release of Mac OS X 10.5.3 iPhone users (and anyone else) can now sync their Address Book contacts with Google Contacts. Within the Address Book Preferences, under General, you now have the option to Synchronize with Google.
Just check the box, it will ask you for your Google account and password and from now on every time you sync your iPhone your address book will also be synced with Google.
It really looks like Apple is trying to make it as easy as possible for users to get their data wherever they want it. Although many people think that Apple never wants to play with anyone else this clearly shows that Apple is interested in doing what consumers want.