Voice and Data in today's world can no longer be separated into different camps. Historically we had a separate set of wire that carried voice traffic and another one for data. Later, we used a data circuit and split it into different pieces. We had expensive equipment on both ends of the network that would split the voice and data into two different pipes.
Today we are able to send the data for your applications via IP networks and the Internet. So some smart guys got together and said, "can't we make the voice information look like an application as well." The advent of VoIP or voice over IP is the result. In not technical terms, the voice call now becomes another piece of data on the data network that you use for your applications.