Earlier this week, Microsoft released an optional update for Windows Phone SDK that will add two new Windows Phone 7.8 emulator images to your existing Windows Phone SDK installation. These two emulator images enable you to fully test how your Windows Phone 7.5 app’s Live Tiles will look and behave on a device running Windows Phone 7.8.
Now is a great time to update your apps to take advantage of the new tile experience, but also will enable you to be ready as your customers arrive on 7.8.
To add the new emulators to your PC, download the Windows Phone SDK Update for Windows Phone 7.8 from the Microsoft Download Center. The update requires that the WPSDK is already installed, and supports versions 7.1 and 8.0.
Download : SDK Update for Windows Phone 7.8
Refresh existing apps for Windows Phone 7.8:
As you evaluate the new 7.8 update for the Windows Phone SDK, consider refreshing your existing 7.x apps. Microsoft recently outlined on the Windows Phone Developer blog some simple tips to make it easy for you to add Windows Phone 8 Live Tile functionality to your 7.1 app so that when it is run on a Windows Phone 7.8 or 8 device, it “lights up” the new templates.
While you’re in the process of updating your apps, make sure to take advantage of the widest audience possible for your app. Windows Phone now reach consumers in 95 markets; if you haven’t already, visit Dev Center and submit your current Windows Phone 7 apps for worldwide distribution to ensure you are ready for new phones running Windows Phone 7.8 and 8.
Adding Windows Phone 7.8 and 8 tile functionality to Windows Phone OS 7.1 apps