Xamarin Mobile and Windows Phone 8
Xamarin.Mobile is a C# based toolchain which (currently) abstracts the contacts, camera, and geo-location APIs across iOS, Android and Windows platforms. This article provides a brief overview of the tool.
Windows Phone 8
Xamarin allows developers to create apps in C# and .NET, and create "native appearing" code on all supported platforms, and also to call native code. There is an excellent overview of the concept in the document Building Cross Platform Applications.
Licensing is commercial, though there is a free option suitable for basic evaluation.