If you are a programer and need to build your softphone in VB.NET you could try out the following sample program: www.voip-sip-sdk.com/p_179-windows-forms-softphone-vb-net-voip.html It's based on an sdk which is written in .Net and that's why it insures flexibility including even further developments. I don't want to advertise just share my good experiences with you related to development. What's your opinion?