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The first published telephone test was John Hilliard's “Twentieth Century Telepathy” in The February 1905 Sphinx, Vol. 3 No. 12, p. 150. Bill Kalush has found a reference to Houdini having performed such a routine in the 1890s.
Rufus Steele's Card Tricks You Will Do (1926, p. 22) includes “Mind Reading by Telephone” by Bill Bournau, which has the earliest instance, discovered to date, of coding by including or excluding actions made by the spectator during the call to the medium. This predates Read's “Calostro Act” by six years, and Annemann's “Weird Wire” by twelve.
(See also Mr. Wizard Telephone Test.)