Official Google Blog: Calendar and contact syncing for iPhone and Windows Mobile devices
http://googleblog.blogspot.com/2009/02/calendar-and-contact-syncing-for-iphone.html

using google calendar with iphone

One advantage of storing information online is being able to access it from anywhere, on any device. Last year we released a tool for Blackberry devices to sync Google Calendar and Gmail contacts with the pre-installed calendar and contacts applications. Today, we're offering more people easy access to their information on the go with two-way calendar and contacts sync for iPhones and Windows Mobile devices, and two-way contacts sync for mobile devices that support SyncML. This will be a particularly handy improvement for people who regularly use Google tools, like corporate employees, university students, and busy families.

look into this?