Starting January 30, 2013, consumers won't be able to set up new devices using Google Sync to build a seamless sync experience for Gmail. Google sync service powered by Exchange ActiveSync has been discontinued by Google but the existing connections will continue to work. Google Calendar Sync has already been discontinued, informed on Google Blog.
Android users aren't affected. For iPhone, iPod and iPad, there's a dedicated Gmail app but Windows Phone 8 users are in trouble. Right now, Exchange ActiveSync is the only option to push email, calendars, and contacts in Windows Phone. There's an email-only option in Windows Phone 8 which set up an IMAP connection to Gmail which doesn't support push. It just sync every 15 minutes at best.
Google has recently revealed that it has no plans to release Gmail app for Windows 8 and Windows Phone 8.