Ebay sellers like to use the word "Prototype" to help boost the bid prices.
Here's a 500D with some lights, switches and jacks added, where the seller dangles the word then cleverly explains that he doesn't "know anything." The photos of the bottom tell the story.
http://www.ebay.com/itm/131642704093 (http://www.ebay.com/itm/131642704093)
Prototype?? Vintage Western Electric 500 Telephone with Added Features
"I don't know anything about this particular phone but it seems special to me. I believe it is an early 1950's Era Prototype of the Bell System. It is a Western Electric Model 500 with accessories. An outlet on its side for Headphones to be plugged in at. Two lights on the front beneath the dial. Unknown how they function. And an On / Off switch under the cradle area. Definitely a fine specimen for your collection."
Seller: 10-32*larry (1079)
Starting bid: US $95.00
Well, in fairness to the seller, "Prototype" has question marks after it, and the "seller notes" appear to be a quote from someone ("Mr. Helpful"?) who contacted him and suggested that it was a "prototype". I don't get the impression that the seller intends to deceive, but is using unsolicited information as "fluff". The only prototype I'm aware of didn't have the standard markings on the bottom, such as Dan/Panther's prototype (http://www.classicrotaryphones.com/forum/index.php?topic=2394.msg31962#msg31962). Without further documentation of it's status as a prototype, I seriously doubt the seller will get the asking price.
Yea, just a modified 500 c/d
I agree. Did anyone notice that the handset isn't original to a 1958 model? It is from a much later phone because it has the center holes in the caps.