From: Richard <legalize at xmission.com>
  Anyone know anything about these? 
Google for AT&T 5620 and/or AT&T BLIT.  The 730 is a descendant.
  Apparently they could be used as X terminals and they
are essentially
 diskless workstations with a 68000 inside. 
They can be regular dumb terminals or "layers" terminals, which is a really
rather interesting, pre-XTerminal remote windowing system worked on by,
among other luminaries, Rob Pike.  As I recall, they came out with an X
cartridge for the 730 since layers never caught on.  I only saw NCR rebadged
X Terminals during my time at AT&T, so I assume the X cartridge didn't catch
on either, even internally.
  Any AT&T 3B2 owners out there have one of these in
a working state? 
Don't think many of them ever made it out of AT&T...at least I've never seen
one in the wild.