Crossword clues for the word: ISDN The word ISDN has appeared as an answer to at least 6 crossword clues on different crossword puzzles. Crossword clues for ISDN Showing 1 to 6 of 6 results Clue(s) High spd. phone line High speed phone line (abbr.) Phone line abbr. Voice/data connection (abbr.) Voice/data connection, abbrev. Voice/data transmission standard (abbr.)