I found a useful solution on how to build a softphone in VB.NET. I can recommend it everyone who wants to get this process quickly. This softphone is based on the SIP implementation of Ozeki VoIP SIP SDK. Available: http://www.voip-sip-sdk.com/p_179-wi...-net-voip.html

The company is responsive, so after purchase I get the necessary help from an assigned engineer. This part was the most valuable for us…
I hope I can help others