1. Open following URL with iPhone Safari.
If it shows like “This device can’t use Google Sync”, then select “Change Language” and select “English (US)”.
2. Select iPhone in the list. (If you already configure Google Sync with other iphone device, Multiple entries will shows up here.)
3. Calendar list on Google Calendar will be shown with check box.
Check the box that you want to use from iPhone, then push SAVE button.