Microsoft has released an update for Windows Phone SDK for Windows Phone 7.8 support. This SDK adds Windows Phone 7.8 emulator support for Windows Phone SDK 7.1 and Windows Phone SDK  8.0.

The Windows Phone SDK Update for Windows Phone 7.8 adds two new emulator images to your existing Windows Phone SDK installation.

  • New Windows Phone Emulator 7.8
  • New Windows Phone Emulator 7.8 256MB

This update supports both the Windows Phone SDK 7.1 and the Windows Phone SDK 8.0.

Using this update, you can provide the Windows Phone 8 Start screen experience in your Windows Phone 7.5 apps. You can also test how your apps will run on Windows Phone 7.8 devices.

Note: Windows Phone SDK 8.0 or Windows Phone SDK 7.1 must be installed before you can install Windows Phone SDK Update for Windows Phone 7.8.

For more information about Windows Phone 7.8, see Windows Phone developer docs.

[Quote from Microsoft Download Center]

Download Windows Phone SDK update for Windows Phone 7.8