Early development

The following is a brief summary of the history of the development of the telephone:
1872 Elisha Gray establishes Western Electric Manufacturing Company.
1 July 1875 Bell uses a bi-directional "gallows" telephone that was able to transmit "voicelike sounds" but not clear speech. Both the transmitter and the receiver were identical membrane electromagnet instruments.
1875 Thomas Edison experiments with acoustic telegraphy and in November builds an electro-dynamic receiver but does not exploit it.
6 April 1875 Bell's US Patent 161,739 "Transmitter & Receiver for Electric Telegraphs" is granted, outlining the concept of multiplexed frequencies.
11 February 1876 Elisha Gray invents a liquid transmitter for use with a telephone, but does not build one.
7 March 1876 Bell's US patent 174,465 for the telephone is granted.
10 March 1876 Bell transmits speech "Mr. Watson, come here, I want to see you." using a liquid transmitter and an electromagnetic receiver. Spilling battery acid was not recorded in his lab notes.
30 January 1877 Bell's US patent 186,787 is granted for an electro-magnetic telephone using permanent magnets, iron diaphragms, and a call bell.
27 April 1877 Edison files for a patent on a carbon (graphite) transmitter. The patent 474,230 was granted May 3, 1892 after a 15 year delay due to litigation. Edison was granted patent 222,390 for a carbon granules transmitter in 1879.