Oi (Oi S.A.) is a company in the telecommunications sector in Brazil, considered the largest fixed-line telephone operator and the fourth largest in mobile telephony in the country. In relation to South America, Oi stands out as the largest telecommunications company.

Present in more than 5 thousand Brazilian municipalities, Oi has over 57 million customers across the country. In some cases, the telephone company is the only one in the municipalities, recording a total reach of 40% in areas without competition. On the Brazilian stock exchange, Oi has shares traded under the ticker OIBR3.

Among the products offered by the company, the following stand out: fixed and mobile telephony services, broadband, pay TV, data transmission, and internet service provider. Additionally, Oi also offers corporate and wholesale services, which include transport network and international backbone products.

Furthermore, the company's areas of coverage are divided into:

• Region I: Northeast, Southeast (except São Paulo), and North (except AC, RO, and TO);

• Region II: Midwest, South, and the states of AC, RO, and TO;

• Region III: São Paulo;

• Region IV: all of Brazil.

The history of Oi began in 1998, after Telebrás was privatized and divided into twelve different companies. With privatization, the company acquired Brasil Telecom, in 2009, which consequently initiated a large fixed-line telephone infrastructure in the country.

Among the twelve divisions was Telemar – Tele Norte Leste S.A which, at the time, owned eight holdings of the mobile telephony concessionaires of Band A. In 2002, Telemar launched Oi, a company specialized in mobile telephony.

With just one year after its launch, Oi already recorded 1.4 million customers and, with that, gained the right to operate long-distance services in the country. In 2006, the company began providing integrated telecommunications services to Antarctica, being a pioneer in offering this type of service.

By 2007, after unifying all the services offered, Telemar transformed Oi into the only company of the group, starting to offer all telecommunications services through Oi S.A.