The Early Television Foundation has many links. [1] There's a sizable history of rotating-machinery mechanical television. It's not hard to do, but it never got very good. You can only light up one pixel at a time, so you're stuck with dim, flickering images.
Scophony and Eidiphor, though, were clever pre-CRT systems with more potential. Eidiphor big-screen television projectors were patented in 1939, and were in use into the 1990s.
Of course this was far technically simpler than "proper" video telephony, as they required dedicated point to point circuits rather than function over a regular phone line. Most of the effort to popularise video-telephony was not the concept itself, but solving the engineering challenges of making it work over the regular phone network and making the devices small and cheap enough. In that respect the booths at the '64 World's Fair would have been impressive demonstrations of progress toward that goal.
Scophony and Eidiphor, though, were clever pre-CRT systems with more potential. Eidiphor big-screen television projectors were patented in 1939, and were in use into the 1990s.
[1] http://earlytelevision.org/mechanical_gallery.html