A: Assuming you already have the iPhone set up to sync your mail using the ActiveSync service, you only need to do three things.
From your Device:
- Visit http://m.google.com/sync - Log into that account and check the box next to each calendar.
- Open Settings / Mail / Google Account & turn on Calendars
- Open Calendar / Click Calendars (top left) / Check the Calendars you want to show up.