Expanding 4.5 million fixed lines to 20 million in just 12 years, kt introduced universal telephone service to every citizen of Korea, leading the development and advancement of communications services. More recently, kt established an advanced broadband network for the first time in Asia, and launched Korea's first communication satellite 'Mugunghwa (Sharon's Rose)', contributing to making Korea one of the most advanced countries in information and communications. Since becoming a government-funded corporation in 1997, kt changed its business portfolio to focus more on wireless and internet services instead of fixed lines. Taking over Hansol M.com and merging with its subsidiary KTF, kt expanded its business scope and included mobile communication as its main service. kt became a privately owned company in 2002 and began concentrating on building broadband network. As a result, the company set several new records including the increase of ADSL subscribers to 6 million in just 3 years and played a leading role in the age of digital networking.

ETRI is the largest government funded research institute in Korea, which strives to advance science by means of formulating innovative ideas; developing new techniques; and training professional individuals in the area of information telecommunications to ultimately enhance social and economical aspects of the modern society.

AT&T Inc. is an American multinational conglomerate holding company headquartered at Whitacre Tower in Downtown Dallas, Texas. It is the world's largest telecommunications company, the largest provider of mobile telephone services, and the largest provider of fixed telephone services in the United States through AT&T Communications. Since June 14, 2018, it is also the parent company of mass media conglomerate WarnerMedia, making it the world's largest media and entertainment company in terms of revenue. As of 2018, AT&T is ranked #9 on the Fortune 500 rankings of the largest United States corporations by total revenue.

Telefonaktiebolaget LM Ericsson engages in the provision of telecommunications equipment and related services to mobile and fixed network operators. It operates through the following segments: Networks, Digital Services, Managed Services, and Emerging Business and Other. The Networks segment supports all radio-access technologies and offers hardware, software and related services for both radio access and transport. The Digital Services segment provides software and services in the areas of digital business support systems, operational support systems, cloud communication, cloud core, and cloud infrastructure. The Managed Services segment includes networks and information technology managed services, network design and optimization, and application development and maintenance. The Emerging Business and Other segment encompasses emerging business, Iconectiv, Red Bee Media, and Media Solutions. The company was founded by Lars Magnus Ericsson in 1876 and is headquartered in Kista, Sweden.

Nortel Networks has hung up on the telecom sector. Once one of the largest makers of telecommunications equipment in North America, it filed for bankruptcy protection in 2009 and is in the process of liquidating its assets. The company made core network switching, wireless, and optical systems for network operators. Its wireline and enterprise network equipment included systems for digital voice and data switching, routing, and call center communications. Wireless products included cellular base stations and controllers. The company also made such long-haul fiber-optic products as multiplexers. Nortel is currently focused on selling off its remaining businesses and intellectual property and winding down all operations. Today, Nortel's Metro Ethernet Networks segment provides carrier Ethernet switching, optical networking, and multi-service switching products.

The Distribution Systems Research Institute engages in streamlining and standardization of distribution systems. It also provides support for increasing the efficiency of supply chains. The company was founded in 1972 and is headquartered in Tokyo, Japan.

Manufactures telecommunications equipments and network solutions to service providers

Mercury Corp. designs and manufactures telecommunications equipment. Its products include Fiber, Network, Access, and Voice Switch. The company was founded on August 21, 2000 and is headquartered in Incheon, South Korea.

Daewoo Telecom Ltd. is a company headquartered in the South Korea ultimately controlled by the Government of South Korea focused on computers and computer peripheral equipment and software.

Designs and builds a wide range of public and private networks, communications systems and software, and data networking systems, as well as telephone systems and microelectronic components

Ribbon Communications Operating Co., Inc. provides communication solutions. The company is headquartered in Plano, TX.

LG Information & Communication Ltd. provides telecommunication services. It offers switching systems, transmission equipment, wideband digital cross-connect system, fiber loop carrier system, CDMA mobile systems, communications terminals and information networks. The company was founded in 1979 and is headquartered in Seoul, South Korea.

NewStep Networks, Inc. provides service convergence and fixed-mobile convergence software solutions. The company offers FlexConnect solutions that bring the benefits of service convergence to mobile, office, and home phones; and Enterprise Mobility solutions, which feature one button transfer, single number service, automatic reconnect, single voicemail, and voicemail intercept. It also offers Total Mobility solutions that feature FlexConnect Solution and Enterprise Mobility Solutions, and add features designed for enterprise environments. Its customers include enterprises, service providers, equipment makers, system integrators, and business and consumer users. The company was formerly known as Rev D Networks, Inc. and changed its name to NewStep Networks, Inc. in November 2003. The company was founded in 2003 and is headquartered in Toronto, Canada with additional Offices in Canada, the United States, Europe, and Asia. As of June 8, 2009, NewStep Networks, Inc. operates as a subsidiary of Natural Convergence, Inc.

Broadview Networks, Inc. provides communications and IT services. Its products include OfficeSuite UC, OfficeSuite HD Meeting, OfficeSuite Cloud Computing through which the firm helps organizations to connect with customers with local and long-distance voice and data communications, premises-based and patented hosted VoIP systems, data services and a full suite of managed and professional services. The firm's customers include the healthcare, financial services, education and government, professional services and retail industries. The company was founded by Terrence J. Anderson in 1996 and is headquartered in Rye Brook, NY.

NEC Corp. engages in the provision of systems, components, services, and integrated solutions for computing and communications applications. It operates through the following segments: Public Business, Enterprise Business, Telecom Carrier Business, System Platform Business, and Others. The Public Business segment provides system integration (system architecture and consulting), support (maintenance), outsourcing and cloud services, and system equipment for public, medical and financial institutions. The Enterprise Business segment offers information technology solutions for manufacturing, retail, and services. The Telecom Carrier Business segment supplies equipment to telecom carriers for network implementation, along with network control platform systems and operating services. The System Platform Business deals with products from business such as from terminals to network and computer equipment, software products, and service platforms. The Others segment includes smart energy solutions, mobile phones, and lighting equipment businesses. The company was founded by Kunihiko Iwadare on July 17, 1899 and is headquartered in Tokyo, Japan.

SK Telecom Co., Ltd. (Hangul: SK텔레콤 or 에스케이텔레콤) is a South Korean wireless telecommunications operator; it is part of the SK Group, one of the country's largest chaebols. SK Telecom is South Korea's largest wireless carrier: it leads the local market with 50.5 percent share as of 2008. Since its creation in 1984, the company has evolved from a first generation analog cellular system, to second generation CDMA, then to the world's first third-generation synchronized IMT-2000 cellular system. SK Telecom also became the world's first carrier to commercialize HSDPA in May 2006. SK expanded into the landline market by acquiring second-rated fixed-line operator Hanaro Telecom in February 2008.

Provides telephone services