I have found a useful guide on how to connect to a server that is supported by Ozeki VoIP SIP SDK from Silverlight applications. On this page http://www.voip-sip-sdk.com/p_258-si...ient-voip.html
you will find an explanation for the configuration steps and the source code as well.
For this you will need Microsoft Silverlight 4 Tools for Visual Studio 2010. ;)
Manuel Sanches from Spain