Push to Talk on Intranet between two Clients

Project Description:

I need for a project the subsequent:

Two people will communicate on one (max. two) computers through a push to talk (holding down a button for speaking)

The circumstances is that I have clients in the back of the car and I need them to be able to hold down a button and through this push to talk the driver hears the voice of the clients and can converse with them by doing the same push to talk.

There is a lot of existing software using voip ptt for this but I need it simple and clean.

The GUI is only believed to be for example a round Circle that turns green once you push.

Skills required are Software Architecture, VoIP, Software Development