The Free On-line Dictionary of Computing (30 December 2018):

Dataphone Digital Service

    (DDS) The first private-line digital
   service offered by AT&T, with data rates typically at 2.4,
   4.8, 9.6 and 56 kilobits per second.  DDS is now part of
   AT&T's Accunet family of services.  Most LEC (local exchange
   carriers) and IXC (IntereXchange Carriers) offer similar
   services.

   (1995-02-28)