Google just announced a new service for pushing Gmail contacts and Google Calendar updates to mobile devices. For iPhone and Windows Mobile devices Google is using Exchange ActiveSync with some limitations due to the beta nature of the service, but it'll also work on many other devices that support SyncML (a vendor list is here). Google Sync works automatically, and replaces all existing contact and calendar information on the device, so sync-er beware -- we wouldn't let Google get close to our contacts without some serious preflight cleanup and maintenance. Google Apps users can enable the service per domain. There's an explanatory video after the break.
Update: SyncML doesn't "officially" support calendar sync, though experimental types can add "calendar" as a remote database. Sounds like a thrill ride! [Thanks, Nikolay]