For some of us who rely heavily on Google Calendar to get our work and personal lives organized, multiple calendars are inevitable to separate and keep our schedules in order. Microsoft's Windows Phone platform, unfortunately, wasn't able to provide support for multiple Google Calendars during its launch. That is, until now.
The company's Sync team has enabled appointments from multiple calendars on the same Google account to show up, allowing you to have a quick glance at all your calendars. Adding this feature to your Windows Phone, however, won't be done through the Calendar app. Instead, you'll need to go to m.google.com/sync on your Windows Phone device, log in and select the calendars you want to sync onto your device. Up to 25 calendars can be synced, and once you've made your choice, click save and upon the next sync (depending on how frequent you sync your Google account), the calendars will appear on your Calendar app.
On the mail front, it is also possible to search for Gmail messages from the cloud. This means you can search through the Gmail server for your messages, even if they aren't downloaded onto your Windows Phone device.
Some might say that this has been a long wait, especially for the multiple calendar support on Windows Phone. But as they say, it's better late than never.
Source: Windows Phone Blog