You may find this webpage re the history of AT&T's attempt at videophone
service interesting. Especially at the end, it shows a 1990's deskset
that apparently was sold by Sears, and may have been the unit that Danny
Burstein referred to.
https://flashbak.com/the-fantastic-and-troubled-history-of-the-video-phone-404033/
Based on my (now retired) 30 year career in data communications, your
challenge will be to create a video/voice digitizing scheme that can
produce a usable picture & voice needing no more than 2400 bits per
second data rate. There were/are dial-up modems that could create a
2400bps full-duplex data connection over the PSTN (Public Switched
Network). But due to that 2 wire PSTN connection being limited to 3
Kilohertz of analog bandwidth, 2400 digital BPS Full Duplex pushed the
limits of modem technology.
The ITU-T standard for these modems is "V.22bis"
"V.22bis is an ITU-T recommendation extending V.22 with a faster rate
using QAM at 600 baud to carry digital data at 2400 or 1200 bit/s. The
1200 bit/s mode is compatible with V.22."
Good luck.........