Recently some of my frz got new iphone5 from old Android phones.
However, they cannot sync their contacts via gmail the great feature of google account integration.
I thought it would be apple's iOS6 problem so i tried to downgrade to iOS5 or JailBreak. Then we thought Google who recently cut Google Reader might cut this contact feature as well due to the competition to apple's cloud. Therefore, we tried to configure Yahoo and Microsoft's exchange on Android 4.1.2 Jelly Bean but definitely FAILLLLLLLL somehow.
Also some security issues and universality have to be considered.
Lucky we find this google help page later and redo the configuration to all my iOS devices eg. my ipod touch:
Keyword: CardDAV