Electronic Blackboard Transmits Writing Over Phone Lines (1974)

"A new, experimental system devised by Bell Labs may make an old teaching tool more alluring. Called an electronic blackboard, it uses ordinary (and low-cost) telephone lines to send writing that is chalked on a pressure-sensitive surface to any remote point for TV-screen display. The audio portion of a lecture or other presentation can, if needed, be sent via a second phone line, using a portable conference phone available commercially. The system is being tried out at the University of Illinois."
-- Popular Science, June 1974