Unfortunately, I found today that when using ADO.Net in Silverlight 3, some policies weren’t being used preventing cross domain data services from working. There are two policies that can enable cross domain usage. [ClientAccessPolicy.XML and CrossDomainPolicy.XML] each can enable cross domain features, but these are not used by Silverlight 3. There’s a [big workaround] but it’s not what I’m looking for. I’ll catalog this failure with [SL3 not supporting LINQ joins].
Luckily [Silverlight 4] will have “enhanced” support for cross domains and ADO.net.