While
Microsoft first time previewed
Silverlight for
Windows Mobile back in May 2007, it's neither yet available nor has Microsoft
unveiled any details when it will become available. It was only confirmed by
Microsoft that Silverlight for Mobile will be initially launched for Windows
Mobile and S60 smartphones.
Now Microsoft's Windows Mobile team unveiled in its Twitter feed, that it is
most likely that Silverlight for Mobile will be released with the next version
of Windows Mobile (aka Windows Mobile 6.5 which is expected to be available from
summer this year):

Microsoft Silverlight powers rich application experiences and delivers high
quality, interactive video across the Web and mobile devices through the most
comprehensive runtime available on the Web.
On mobile devices, Silverlight provides a homogenous platform for developers
to target a large number of devices as well as deliver rich interactive
applications with vector graphics UI and mobile-optimized media. Further,
Silverlight for mobile enables developers to reuse their existing desktop code,
content and skills and leverages the flexible .NET programming model.
Anyway - an official release date wasn't given yet and it's not clear if it will be
available as a stand-alone download for other Windows Phones too or available as
part of Windows Mobile 6.5 only.
Cheers ~ Arne