I have found a sample program that deals with building a Windows Form Softphone in VB.NET. It provided useful information when I decided to try softphone development. There are code snippets and a good description (In case you are interested: http://www.voip-sip-sdk.com/p_179-vb-net-windows-forms-softphone-voip.html
). I just thought that some of you might find this information useful. This is only an advice and hope it will be a good starting point for beginners.