The .NET SDK versionс that support push initialization and registration (for their native platforms) are respectively the Windows Phone and Windows Store SDK. You can find them along with push notifications samples here
. I feel obliged to underline that these SDKs support subscription for push notifications for their native platforms, they cannot be used in iOS and Android apps.
All versions of the .NET SDK support the sending of push notifications to the devices in your backend project.
Let me know if further questions arise.