Google recently announced that they would end support for Exchange Active Sync for GMail and Google Calendar for free users. Instead they wanted to support open standards like CardDAV and CalDAV instead of Microsoft's proprietary option.Microsoft decided to put an end to the standoff and promised to add support for open standards if they were given the time. Google then extended support for Exchange Activesync until July 31st.
Now it looks like Microsoft will have support for CardDAV and CalDAV in their upcoming GDR2 update for Windows Phone 8.
The following demonstration shows a Nokia Lumia 925 running Windows Phone 8 GDR2 with CardDAV and CalDAV support
Unfortunately according to the source CardDAV and CalDAV only works for Google ccounts and cannot be used with anything else. We are not certain if Microsoft will open the standards for other services in time for the GDR2 release this summer, but we hope that they do.
source - AAWP