Last week finalized the implementation for the support of Visual Basic for the Windows Phone Developer Tools. So now any developer with Visual Basic background can now build Windows Phone application (and Game based on Silverlight).
So to be able to start building Windows Phone application with Visual Basic you need to have Visual Studio 2010 Pro or higher (at this time Visual Studio 2010 Express is not supported). You also require the Windows Phone Developer Tools and the addon for the support of Visual Basic (download here)
For more information, you can read the official post on the Windows Phone Developer Blog here.
Have a good time developing Windows Phone 7 application!