Ralf -- We are actively working on adding support for VS 2012 and Windows Phone 8 in our VSExtensions. Both should be ready by the end of the month. They will surely get included in the next service releases for our Windows Phone components, but those are yet to be scheduled.
If you want to get the VSExtensions as soon as they are ready you could keep an eye out for updates from the Visual Studio Gallery (Link
ManniAT -- Our Windows Phone product installers do not support automatic Visual Studio toolbox registration at the moment, as our preferred method for that does not work for Windows Phone.
At the moment there is a single extra control, which is available for Windows Phone 8 and not available for Windows Phone 7. Could you elaborate on some steps we could use to identify the issue? You could also open a support ticket, so you get swifter reponses.
All the best,
the Telerik team