In my never ending quest to find a first year and last year of manufacture 500, I've noticed a 1991 Cortelco 500 on e-bay right now.
http://tinyurl.com/4tsb5z
Nice color as well. Just not a 2006 model.
I'm just slightly confused, Is the 500 a number used by several different manufacturers, or was it used by Western Electric to identify their phone design.
D/P
From what I know, which is not a lot, the designation of "500" was originally Western Electric's model number for the phone and was then picked up by the other companies that made clones of the phone under their agreement with WE. Cortelco called their model the "500 AS" and they still make a WE 2500 clone that they call the, this is catchy, 2500.
Not only that, but Cortelco also makes a courtesy telephone that looks like a dial-less 2500.