Southeast Michigan was still using telephone exchanges into the 60s. Our number was YUkon 26831. I don't remember when Michigan Bell stopped using the old exchange system, but when my folks sold their old house in the mid 80s the Western Electric wall mount phone still had the old YUkon 26831 number disc in the middle of the rotary dial. Those phones were built like tanks! We had that phone installed when we moved in back in 1965 and to the best of my knowledge it had never needed service in better than two decades.