That certain was an important decision, but the Bell System was still requiring customers to have expensive coupler equipment installed for many years afterwards (that article was from 1974). Those couplers involved transformers that would have made even 56k modems impractical, much less DSL.
For sure, where I lived, the Bell breakup was the dividing line, after which we were allowed to buy phones from someone other than the phone company. I still remember when we got our first non-Bell telephone, though I was a young kid at the time, and it was after Bell broke up. More amusingly, we weren't even in Bell territory; we were served by GTE. That's how wide-ranging the implications of the breakup were. It rocked the industry, and changed things pretty dramatically for the better.