This is the extremely rare Touch-Tone field trial set from 1960. This set was used in technical trials in Cave Spring, VA and Hagerstown, MD, and then in marketing field trials in Findlay, OH and Greensburg, PA in late 1960 and early 1961.
Here is a close-up of the Western Electric set designation. Notice it appears that this set was built on what was originally a normal 500 set base.
A full view of the bottom of this set.
A view with the cover removed, and a nice closer-up view of the key pad.
A side view of the inside of the set with the dial still mounted.
A view of the rear of the field-trial set's key pad.
(Info about the the 1960 Touch-Tone field trial thanks to paul-f.com.)