See http://www.chrissearle.org/google_ios_caldav_carddav for info on switching to a CalDAV/CardDAV setup.
Setting up calendars to sync from google apps to iOS turned out to be harder than I expected.
I had already set up a gmail iOS mail/cal/contacts account on the iPhone. But that only gets the primary calendar.
Calendar & Contacts Sync: Choosing Which Calendars to Sync talks about going to m.google.com/sync - but that just throws back that this isn't supported on your phone.
Google Sync: Set Up Your Apple Device for Google Sync suggests to use an exchange account instead. This didn't seem to help.
However - after a lot of wandering thru the forums I stumbled across this link:
When I logged in there - it listed all my google calendars. I then simply checked them off and they then just turned up on my iPhone as expected.