Source : Free On-Line Dictionary of Computing

Digital Simultaneous Voice and Data
     
         (DSVD) A technique supported by some {modems}
        for multiplexing compressed speech with digital data for
        transmission over a normal telephone line.
     
        DSVD isn't standardised yet, so generally you have to have the
        same make of modem at both ends for it to work.
     
        [How does it work?  Which modems?  References?]
     
        (1997-06-05)