I just looked at the MS documentation on the new Silverlight APIs for Mango:
New Silverlight APIs
And there is no change in the System.SereviceModel namespace, so I suspect the answer is no. This was only added in Silverlight 4.0, and even then Silverlight 4.0 had to have netTcpBinding security mode for "No" for it to work.
Silverlight for Windows Phone is based on Silvrlight 3.0.
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