Well it looks like Stromberg-Carlson manufactured one of the first tone ringers, no.95, in the 1960s, that was used originally in their 1600 series set, The Petite Phone, for the Independent Telephone Companies. This was Stromberg-Carlson's version of the WECO Princess phone, used in the Bell System. If you remember, the first Princess had no internal ringer. Since the no.95 tone ringer was an accessory, Stromberg-Carlson made it available for their 1700 series key telephones (multiline), which was used with the 1A1 and 1A2 KTS. So as far as the first, it was not the Bell System! It was an Independent Telephone manufacturer, not part of the Bell.
RLSbutton,
You should broaden your telephony research history to include the Independent Telephone Industry. A lot of stuff was invented by the Independent Telephone people before the Bell did. Northern Electric's SL-1 phone, the QSU series, came after Stromberg-Carlson's no.95 tone ringer.
Hope this helps!
....JIM....