In 1875, Alexander Graham Bell invented the telephone, leading to the formation of the Bell System under AT&T in the United States.

Alexander Graham Bell and Elisha Gray filed patent documents for telephony devices on the same day in Washington, D.C. Bell was granted the patent for the telephone on March 7, 1876, leading to the formation of the Bell Telephone Co.

The Bell Telephone Company was established in 1877 by Alexander Graham Bell and his father-in-law, Gardiner Greene Hubbard. It was the beginning of the telephone industry in the United States.

The American District Telegraph Company was formed in St. Louis in 1878, which later played a role in the history of AT&T.

The National Bell Telephone Company was established in 1879, succeeding the Bell Telephone Company. It later became the American Bell Telephone Company in 1880.

American Telephone and Telegraph Company was formally incorporated on March 3, 1885. It aimed to create a nationwide long-distance network with a commercially viable cost-structure.

In 1894, competition in the telecommunications industry increased, leading to American Telephone and Telegraph Company taking over various operations to strengthen its position.

An advertisement for the American Telephone and Telegraph Company was featured in 1895, showcasing the services and offerings of the company.

On December 30, 1899, the American Telephone and Telegraph Company bought the assets of American Bell, making AT&T the parent company of the Bell System.

In 1907, AT&T president Theodore Vail formulated the principle that the telephone would operate most efficiently as a monopoly providing universal service, a concept that shaped AT&T's role as a regulated monopoly for many years.

In 1913, American Telephone resolves an antitrust lawsuit by becoming a government-approved monopoly. Despite this, it allows independent phone companies to connect to its long-distance network.

In 1915, American Telephone further solidifies its position as a monopoly in the telecommunications industry, maintaining control over the long-distance network while permitting connections from independent phone companies.

In 1916, American Telephone was added to the Dow Jones industrial average. Over time, it became one of the most widely held stocks due to its perceived safety.

Southwestern Bell Telephone Company was established in 1920 after a series of mergers expanding services to several states, later becoming a subsidiary of American Telephone and Telegraph Company.

In 1925, Bell Labs is established as the research and development arm of American Telephone and Telegraph Company (AT&T), focusing on innovations in communication technology.

In 1927, AT&T inaugurated commercial transatlantic telephone service to London using two-way radio, marking a significant milestone in international communication.

In 1938, the president of AT&T in New York announced the commencement of transatlantic phone service using radio signals, connecting London and New York. The phone call had to travel over 850 miles of land and 6,300 miles of ocean, occasionally facing interruptions from static.

The first mobile phone was developed in 1946, marking a significant advancement in telecommunications technology.

In 1956, AT&T introduced the first transatlantic submarine telephone cable, TAT-1, improving communication between Europe and the United States.

In 1968, the Federal Communications Commission allowed the Carterfone and other devices to be connected directly to the AT&T network, opening up the market to numerous products like answering machines, fax machines, cordless phones, and computer modems.

In 1974, the U.S. government initiated an antitrust suit against AT&T due to changes in telecommunications. The suit aimed to separate AT&T's local exchange services, considered a natural monopoly, from other competitive areas like long distance and research.

On January 8, 1982, the United States v. AT&T antitrust suit was settled, leading to the breakup of AT&T. AT&T agreed to divest its local exchange service operating companies, resulting in the formation of the 'Baby Bells'.

In 1983, AT&T Inc. was forced to divest its local exchange service operating companies due to an antitrust lawsuit. This led to the breakup of the company into seven regional Bell operating companies.

On January 1, 1984, the divestiture of the Bell System took place, leading to the end of the monopoly. AT&T was restructured, and seven regional Bell operating companies were established, changing the landscape of the telecommunications sector.

In 1985, James E. Olson became president of AT&T and initiated job cuts within the information division to enhance profitability.

In 1991, Western Electric was renamed AT&T Technologies and underwent restructuring, with divisions focusing on specific customer groups. AT&T also acquired NCR Corporation but later divested it.

In 1992, AT&T moved its corporate headquarters to San Antonio from St. Louis, reflecting a shift in its operational base.

In 1993, AT&T made a significant move by acquiring McCaw Cellular Communications for $12.8 billion, marking its entry into the cellular telephone business.

In 1996, Congress deregulated the telecommunications industry, allowing for more competition and acquisitions within the sector.

In 1997, SBC Communications Inc. merged with Pacific Telesis Group, expanding its telecommunications operations and market presence.

SBC Communications Inc. acquired Ameritech Corporation in 1999, further strengthening its position in the telecommunications industry.

In 2000, AT&T acquired the nation's No. 2 cable television company, further expanding its presence in the media and telecommunications industry.

On July 9, 2001, AT&T spun off AT&T Wireless Services in the world's largest initial public offering (IPO) at that time. This move aimed to restructure AT&T's business units and enhance its focus on mobile services.

In 2004, the U.S. government eliminated equal access regulations, impacting long-distance phone companies' access to regional Bell carriers' networks. This change prompted AT&T to shift away from residential telephone services and focus on broadband-based offerings like AT&T CallVantage.

SBC announced the acquisition of AT&T Corporation for over $16 billion, marking the beginning of a series of merger talks and approvals by various regulatory bodies.

On November 18, 2005, SBC Communications acquired its former parent company, AT&T Corporation, for $16 billion. This led to SBC adopting the more recognizable AT&T name and brand, while the original AT&T Corporation continued to exist as a subsidiary.

On December 30, 2005, the merged entity of SBC and AT&T Corp. was launched as AT&T Inc., marking a significant milestone in the company's history.

On June 21, 2006, the San Francisco Chronicle reported that AT&T had updated its privacy policy, asserting ownership of customers' confidential information and the right to use it for various purposes, sparking privacy concerns.

On December 29, 2006, AT&T completed the acquisition of BellSouth Corporation after receiving FCC approval. This transaction allowed AT&T to consolidate ownership and management of Cingular Wireless.

On June 1, 2007, Woodbury Telephone merged with Southern New England Telephone, impacting the regional telecommunications landscape.

National Intelligence Director Mike McConnell confirmed in August 2007 that AT&T was one of the telecommunications companies aiding the government's warrantless wire-tapping program, raising questions about privacy and surveillance.

On November 8, 2007, former AT&T technician Mark Klein revealed that all Internet traffic passing through AT&T lines was copied into a secure room accessible only to employees with NSA clearance, highlighting concerns about surveillance and privacy.

AT&T announced the relocation of its corporate headquarters from San Antonio to Dallas, emphasizing better access to customers, technology partners, and global operations.

AT&T announced the cutting of 12,000 jobs due to economic pressures and organizational restructuring.

AT&T acquired Wayport, Inc., a major provider of internet hotspots in the U.S., expanding its public Wi-Fi deployment to 20,000 hotspots.

In 2009, AT&T faced accusations of discriminating against local public-access television channels by implementing restrictions that hindered audience reach and functionality, sparking concerns about access to diverse media.

In June 2010, Goatse Security discovered a vulnerability in AT&T's system that exposed email addresses of customers using the Apple iPad on AT&T's 3G network. The security flaw allowed access to email addresses without requiring a password.

AT&T announced its intention to acquire T-Mobile USA for $39 billion, a move that faced regulatory scrutiny and generated mixed reactions from various stakeholders.

In March 2012, the U.S. federal government filed a lawsuit against AT&T for violating the False Claims Act by enabling fraudulent use of IP Relay calls. AT&T was accused of seeking federal payment for calls made by ineligible international callers for fraudulent purposes.

On December 17, 2013, AT&T announced plans to sell its Connecticut wireline operations to Frontier Communications.

On May 18, 2014, AT&T announced the purchase of DirecTV for $48.5 billion to increase market share in the pay-TV sector and access fast-growing Latin American markets.

On October 25, 2014, Frontier Communications assumed control of the AT&T landline network in Connecticut, following regulatory approval and a significant business deal.

On November 7, 2014, AT&T revealed its plans to acquire Mexican carrier Iusacell, expanding its presence in the international telecommunications market.

On April 28, 2015, AT&T fired Aaron Slator, President of Content and Advertising Sales, for sending racist text messages. This led to a defamation lawsuit against Slator and protests against alleged systemic racial policies at AT&T.

On February 13, 2016, AT&T, formerly known as Ma Bell, underwent a rebranding. The company has a long history dating back to the late 19th century.

On October 22, 2016, AT&T revealed a $108.7 billion deal to purchase Time Warner, aiming to expand its media holdings.

On November 8, 2017, the Department of Justice informed AT&T and Time Warner that they must sell either DirecTV or Turner Broadcasting System for approval of their $84.5 billion merger.

On November 20, 2017, the Assistant Attorney General filed a lawsuit to block the AT&T-Time Warner merger, citing concerns about competition and consumer impact.

In January 20, 2018, AT&T reached an agreement to acquire Time Warner for $85.4 billion. This deal would create a massive company capable of producing and distributing content through various platforms.

In March 2018, AT&T restructured into four main units: Communications, WarnerMedia, AT&T Latin America, and Advertising and Analytics.

On April 18, 2018, AT&T canceled the IPO for DirecTV Latin America due to market conditions.

On May 11, 2018, the CEO of AT&T revealed that the company had paid $600,000 to Essential Consultants LLC for insights on the new administration, describing it as a 'big mistake'.

On June 12, 2018, U.S. District Court Judge Richard J. Leon ruled in favor of the AT&T-Time Warner merger, allowing the deal to proceed.

In early 2019, the Democratic House Judiciary requested records related to the AT&T-Time Warner merger from the White House.

On April 24, 2020, John Stankey replaced Randall L. Stephenson as CEO of AT&T, amidst concerns over the company's debt from acquisitions.

A bombing in Nashville, Tennessee, on December 25, 2020, caused AT&T service outages across the U.S., primarily in Middle Tennessee.

On February 25, 2021, AT&T announced the spin-off of DirecTV, U-Verse TV, and DirecTV Stream into a separate entity, selling a 30% stake to TPG Capital.

On May 17, 2021, AT&T agreed to purchase Time Warner for $85.4 billion.

On December 21, 2021, AT&T agreed to sell Xandr to Microsoft, completing the deal in June 2022.

In 2022, AT&T Inc. merged its equity stake in WarnerMedia with Discovery, Inc. to create Warner Bros. Discovery, divesting its media arm.

On February 22, 2024, a widespread cellular service disruption occurred in the United States, affecting millions of users. The outage led to AT&T customers being unable to connect to emergency services, sparking investigations into a possible cyber attack by the FBI and Department of Homeland Security. AT&T later attributed the disruption to a server update timing issue and compensated users for the inconvenience.