If I hit TBR once, the dial tone drops. If I hit it three times, I hear a rapid busy signal. WTF?
Thanks for finding the model number. I was tempted to open the case but I'm worried it might not close because some barbarian has weakened one of the edge clips. No, wait: that was me!
The amount of triple channel gasketing on the units really make me wonder. I've only seen that sort of care taken on marine electronics. It may not be submersible, but it's highly water resistant. Their PE945 unit is waterproof and floats as well. Don't ask me why I am obsessed with whether it's dunkable!
http://72.14.203.104/search?q=cache:Vqo3eJHgdeYJ:
"Up for auction is a Used Progressive Electronics Model 385 linemen's telephone butt set. It has a Tone or Pulse switch, a talk or monitor switch, last number redial, continuous line polarity indication, waterproof shock-resistant case, belt clip and Mueller/ JS Popper alligator clips with red and black insulating boots."
No info yet on TBR - they seem to use the convention LNR for "Last Number Redial" so it may be for some other function. Highly possible that it's non-functioning, hence the low cost. I'll keep looking.
-- Bobby G.