Timeline of the telephone

11 February 1876: Elisha Gray invents a liquid transmitter for use with a telephone, but he did not make one.
14 February 1876, about 9:30 am: Gray or his lawyer brings Gray's patent caveat for the telephone to the Washington, D.C. Patent Office (a caveat was a notice of intention to file a patent application. It was like a patent application, but without a request for examination, for the purpose of notifying the patent office of a possible invention in process).
14 February 1876, about 11:30 am: Bell's lawyer brings to the same patent office Bell's patent application for the telephone.  Bell's lawyer requests that it be registered immediately in the cash receipts blotter.
14 February 1876, about 1:30 pm: Approximately two hours later Elisha Gray's patent caveat is registered in the cash blotter. Although his caveat was not a full application, Gray could have converted it into a patent application and contested Bell's priority, but did not do so because of advice from his lawyer and his involvement with acoustic telegraphy.  The result was that the patent was awarded to Bell.[5]
7 March 1876: Bell's U.S. Patent, No. 174,465 for the telephone is granted.
10 March 1876: Bell first successfully transmits speech, saying "Mr. Watson, come here! I want to see you!" using a liquid transmitter as described in Gray's caveat, and Bell's own electromagnetic receiver.
16 May 1876: Thomas Edison files first patent application for acoustic telegraphy for which U.S. patent 182,996 was granted October 10, 1876.
25 June 1876: Bell exhibits his telephone at the Centennial Exposition in Philadelphia, where it draws enthusiastic reactions from Emperor Dom Pedro II of Brazil and Lord Kelvin, attracting the attention of the press and resulting in the first announcements of the invention to the general public.
10 August 1876: Alexander Graham Bell makes the world's first long-distance telephone call, over a distance of about 6 miles, between Brantford and Paris, Ontario, Canada.
1876: Hungarian Tivadar Puskas invents the telephone switchboard exchange (later working with Edison).
9 October 1876: Bell makes the first two-way long-distance telephone call between Cambridge and Boston, Massachusetts.
October 1876: Edison tests his first carbon microphone.
1877: The first experimental Telephone Exchange in Boston.
20 January 1877: Edison "first [succeeds] in transmitting over wires many articulated sentences" using carbon granules as a pressure-sensitive varying resistance under the pressure of a diaphragm.[6]
30 January 1877: Bell's U.S. Patent No. 186,787 is granted for an electromagnetic telephone using permanent magnets, iron diaphragms, and a call bell.
4 March 1877: Emile Berliner invents a microphone based on "loose contact" between two metal electrodes, an improvement on Reis' Telephone, and in April 1877 files a caveat of an invention in process.
April 1877: A telephone line connects the workshop of Charles Williams, Jr., located in Boston, to his house in Somerville, Massachusetts at 109 Court Street in Boston, where Alexander Graham Bell and Thomas Watson had previously experimented with their telephone. The telephones became No. 1 and 2 in the Bell Telephone Company.[7]
27 April 1877: Edison files telephone patent applications. U.S. patents (Nos. 474,230, 474,231 and 474,232) were awarded to Edison in 1892 over the competing claims of Alexander Graham Bell, Emile Berliner, Elisha Gray, Amos Dolbear, J.W. McDonagh, G.B. Richmond, W.L.W. Voeker, J.H. Irwin and Francis Blake Jr.[8] Edison's carbon granules transmitter and Bell's electromagnetic receiver are used, with improvements, by the Bell system for many decades thereafter.[9]
4 June 1877: Emile Berliner files telephone patent application that includes a carbon microphone transmitter.
9 July 1877: The Bell Telephone Company, a common law joint-stock company, is organized  by Alexander Graham Bell's future father-in-law Gardiner Greene Hubbard, a lawyer who becomes its first president.
6 October 1877: the Scientific American publishes the invention from Bell – at that time still without a ringer.
25 October 1877: the article in the Scientific American is discussed at the Telegraphenamt in Berlin
12 November 1877: The first commercial telephone company enters telephone business in Friedrichsberg close to Berlin[10] using the Siemens pipe as ringer and telephone devices build by Siemens.
1 December 1877: Western Union enters the telephone business using Edison's superior carbon microphone transmitter.
28 January 1878: The first commercial North American telephone exchange is opened in New Haven, Connecticut.
4 February 1878: Edison demonstrates the telephone between Menlo Park, New Jersey and Philadelphia, a distance of 210 kilometres (130mi).
14 June 1878: The Telephone Company (Bell's Patents) Ltd. is registered in London. Opened in London on 21 August 1879, it is Europe's first telephone exchange, followed a couple of weeks later by one in Manchester.[11]
12 September 1878: the Bell Telephone Company sues Western Union for infringing Bell's patents.
1878: The first Australian telephone trials were made between Semaphore and Kapunda (and later Adelaide and Port Adelaide) in South Australia.[12]

Question: When were telephones first used in homes?
Answer: April 1877