The Collaborative International Dictionary of English v.0.48:

Speaking \Speak"ing\, a.
   1. Uttering speech; used for conveying speech; as, man is a
      speaking animal; a speaking tube.
      [1913 Webster]

   2. Seeming to be capable of speech; hence, lifelike; as, a
      speaking likeness.
      [1913 Webster]

   A speaking acquaintance, a slight acquaintance with a
      person, or one which merely permits the exchange of
      salutations and remarks on indifferent subjects.

   Speaking trumpet, an instrument somewhat resembling a
      trumpet, by which the sound of the human voice may be so
      intensified as to be conveyed to a great distance.

   Speaking tube, a tube for conveying speech, especially from
      one room to another at a distance.

   To be on speaking terms, to be slightly acquainted.
      [1913 Webster]

WordNet (r) 3.0 (2006):

speaking tube
    n 1: a tube for conveying the sound of a voice from one room to
         another