This sort of research continued on the Internet, and provided the impetus for dividing the transport and network layers and the invention of UDP. Internet phone calls are often referred to as voice over IP or VoIP calls.
Internet telephony remained a research topic until February 1995 when a small Israeli company, VocalTec Communications, released a free program called InternetPhone. Hobbyists began making free, low quality, calls, and InternetPhone soon had imitators.
At first the quality of Internet phone calls was quite poor. One limitation was modem speed. There were no broadband connections to homes in those days, and many modems had a top speed of 28.8 kbps.
Computer sound cards were also a bottleneck. Analog voice data had to be digitized and packetized to be sent, then converted back to analog at the receiving end. The hardware delays due to this analog-to-digital and digital-to-analog conversion were significant.
To make matters worse, early sound cards were half duplex which meant they could send and receive, but not at the same time. Only one person could speak at a time, making conversations awkward.
Finally, transport times across the Internet varied considerably, requiring buffers for voice packets, but these introduced further delays. (Variation in packet transport time is called jitter).
Using the 1995 Internet and PC and sound card hardware, VoIP calls had delays, echoes, and dropouts and only one person could speak at once. It was easy to dismiss VoIP as a hobbyist toy.
But, the Internet has improved over the years as has host hardware. Today, VoIP quality is on a par with switched telephone calls, and being integrated with other Internet applications.