Careful, you might drag these Kindles into the 19th century:
I guess they didn't have BlueTooth headsets in 1879.
Or later, like the 20th century:
They (AT&T) boasted of (up to) 10 frames/second but 3 frames/second was more common in the real world.
So except for the slowest model - your already there - slow-scan video calls on a "book" isn't all that bad.
Might have to re-awaken that SIP thread (which seemed to die off at finding matching audio library versions).