How to sync multiple calendar between google and your iphone / ipad

Well, it's not obvious, so

Configure your phone to sync over exchange :

Address: xxx@gmail.com
Domain: blank
Username: xxx
Password: yyy

Click next, then enter this in server :

Server: m.google.com

So your iPhone / iPad will not be sync with your google account.

The open safari on this page : http://m.google.com/sync

Change the language to English UK (to have the latest version).

The select your iDevice in the list, and add all calendar you want. Save it.

Now it work fine on your iPhone, all calendar are sync.