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. For examp

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. For example, see: https://www.ll.mit.edu/news/ieee-milestone-packetspeech.html https://www.ll.mit.edu/news/ieee-milestone-packetspeech.html And: https://www.researchgate.net/profile/Stephen_Casner/publication/262346296_A_packet-switched_multimedia_conferencing_system/links/0deec525eb13ef13bc000000.pdf https://www.researchgate.net/profile/Stephen_Casner/publicat... And: https://qos.ittc.ku.edu/research/thesis/documents/michael_todd_gardner_thesis.pdf https://qos.ittc.ku.edu/research/thesis/documents/michael_to... etc.