SIP/IAX extension to WhatsApp

I am looking for a freelancer to help me develop a system that will integrate a SIP/IAX extension with WhatsApp. This system will provide voice communication for one-to-one calls, between two users, not for group calls. The extension will enable secure voice calls between users of different messaging platforms, so that I can continue to have conversations with my contacts on SIP/IAX while also using WhatsApp. The system should be a fully secure and reliable integration, capable of securely achieving a seamless exchange of communications. In addition, the system should be able to handle large volumes of calls without any downtime or lag. Once complete, the system should be able to meet all of my needs and expectations. It is better to be integrated as Windows App.