If you read, for example, Jason Langridge's blog (Microsoft Windows Mobile team)
http://blogs.msdn.com/jasonlan/
you can get to know that Microsoft and some OEM's are doing the R&D job sometimes tight and sometimes completely offline, but certainly never external.
Based on the expertise You obviously have, I guess You know all relevant developers' web sites and communities where You can get upfront and in-depth background information, often including early bits and pieces of software.
All that might be good for testing, but does not grant for going into final releases and may often even be puzzled together from different sources.
So, very likely not what You are looking for anyway, right?