establish phone-to-phone call over sip account at a betamax provider in vb.net?

Question

Hello. I use webcalldirect to phone foreign countries. Webcalldirect is a voip service from betamax. I would like to write a app, which offers me to start phone-to-phone calls. The clientapp from webcalldirect offers such functionality, but since there are no extras included, I would like to write my own. There is no need for pc-to-phone calling, since I always use my housephone. I would just need to establish phone-to-phone calls. I've got all the sip account infos for use in a sip-software or sip-hardware phone from webcalldirect.

Anybody with an idea how to start a phone-to-phone call in vb.net?

Greetings

Emvelo