The Windows Phone 8 platform was designed to also run Windows Phone 7.x applications. With the new SDK, most developers can very easily continue to deliver applications for both Windows Phone 7 and Windows Phone 8 by compiling to Windows Phone 7. However, in recent testing our team has discovered a few scenarios where existing applications do not perform as well on Windows Phone 8 as they did on Windows Phone 7, and therefore require some optimization. We believe most developers will want to fine tune the experience using the new SDK.
Please refer to the following resources for common questions:
Please contact Developer Support with any additional questions.