There's a fair amount of work on voice over IP and packet switched networks that predates (by a wide margin) 1994, including connections to the PSTN.<p>For example, see: <a href="https://www.ll.mit.edu/news/ieee-milestone-packetspeech.html" rel="nofollow">https://www.ll.mit.edu/news/ieee-milestone-packetspeech.html</a><p>And: <a href="https://www.researchgate.net/profile/Stephen_Casner/publication/262346296_A_packet-switched_multimedia_conferencing_system/links/0deec525eb13ef13bc000000.pdf" rel="nofollow">https://www.researchgate.net/profile/Stephen_Casner/publicat...</a><p>And: <a href="https://qos.ittc.ku.edu/research/thesis/documents/michael_todd_gardner_thesis.pdf" rel="nofollow">https://qos.ittc.ku.edu/research/thesis/documents/michael_to...</a><p>etc.