The big deal was the vertical split between local (baby bells) an long distance (at&t). It then became possible to easily switch your long distance carrier, which lead to intense competition and lower prices. Local exchange service remained a monopoly, but most jurisdictions had fairly strict tariffs for rates. Later, the telecom act of 1996 opened up to competitive exchange carriers using the existing lines and buildings; would have been nice if the FCC had enforced that for internet too :(