After upgrading my brides iPhone 3GS to iOS 4 and getting my new iPhone 4, I noticed that Google Calendar was now only syncing our primary calendars. After several attempts at trying to get all the calendars to sync, I’ve finally found a solution.

YMMV, but this is what has worked for me.

1. Starting with no accounts on the phone.
2. Add a new Gmail account (this is for your email, I don’t sync contacts)
3. Add a new Exchange account (this is for your calendar).
4. Open Calendar and validate that it is pulling down your primary calendar. Close calendar.
5. Follow these instructions from Google.
   1. I had multiple “devices” listed, and chose the device that had the most current “Last sync” date/time.
6. Close Safari
7. Open Settings
8. Open Mail, Contacts, Calendars
   1. Open Fetch New Data
   1. Turn Push On
   2. Open Advanced
      1. Set your Calendars to Push
9. Close Settings
10. Open Calendar and wait for it to sync
    1. I had to force quit calendar from the “running” programs dock and then re-open calendar before it would start to sync with the new settings.