This letterbook covers the period September 1886-January 1888. Most of the correspondence is by Alfred O. Tate. There are also letters by Samuel Insull. The book contains correspondence relating to the commercial development of Edison's phonoplex telegraph system in North America and the United Kingdom. Included also are a cost estimate for a phonoplex installation on the Norfolk & Western Railway and a list of Midwest railroads that were potential customers for the phonoplex. Among the recipients are numerous railroad and telegraph companies including the Baltimore & Ohio Telegraph Co.; the Chicago, Burlington & Northern Railroad; the Chicago & Grand Trunk Railway; the Great Northwestern Telegraph Co.; the Lehigh Valley Railroad; the Norfolk & Western Railway; and the Philadelphia, Reading & Pottsville Telegraph Co. The front cover is labeled "Phonoplex Book Sept 16, 1886--." The spine is labeled "1886-1888 Phonoplex Book" and is stamped "Letters." The book contains 695 numbered pages and an index. There are also numerous groups of unnumbered pages inserted into the book between the numbered pages. Pages 625-695 are blank. Approximately 60 percent of the book has been selected.