Follow these links for all the details:
- Google Mobile - Sync: The overview
- Sync: Contacts Upload via iTunes (PC): Backup your current iPhone contacts
- Sync: Set Up Your iPhone or iPod Touch: Set up Google Mobile Sync
- Sync: Synchronizing Contacts or Calendar: A brief note on sync
- Sync: Choose Which Calendars to Sync: Select up to five Google Calendars to sync with your iPhone
- Sync: Can I Still Sync with iTunes?: It's all OTA from here!