All of this talk about Step by Step reminds me of Nates, Quebec Canada. Nates (pronounced "Not"), as far as telephone fans are aware of, was the last electro-mechanical switching system in the PSTN. It went digital in 2002.
The last ones in the United States that I'm aware of were old GTE and United Telephone in the midwest and Hawaii. All of these went digital in 1999.
For a fully narrated review of Nates, check out Phone Trips at:
formatting linkFor some sample sounds of Nates and other Step by Step switching systems, check out Telephone World's old (vintage) sounds section: