425

Filed by Portugal Telecom, SGPS, S.A.

pursuant to Rule 425 of the Securities Act of 1933

Subject Companies: Portugal Telecom, SGPS, S.A.

Commission File No.: 001-13758

Oi S.A.

Commission File No.: 001-15256

This communication is not an offering document and does not constitute an offer to sell or the solicitation of an offer to buy any securities or a solicitation of any vote or approval in any jurisdiction in which distribution of an offering document or such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of that jurisdiction.

This communication contains information with respect to (1) the proposed merger of shares (incorporação de ações) between Oi S.A. (“Oi”), on the one hand, and Telemar Participações S.A. (“CorpCo”), on the other hand, and/or (2) an alternative structure under analysis to the proposed merger (fusão por incorporação) of Portugal Telecom, SGPS, S.A. (“Portugal Telecom”) with and into CorpCo (these transactions, together with any other transactions related thereto, the “Business Combination”).

In connection with the Business Combination, CorpCo or one of its affiliates plans to file, and Portugal Telecom may also file, with the SEC (1) one or more registration statements on Form F-4, containing a prospectus or prospectuses which will be mailed to shareholders of Oi and/or Portugal Telecom, as applicable (other than non-U.S. persons as defined in the applicable rules of the SEC), and (2) other documents regarding the proposed Business Combination.

We urge investors and security holders to carefully read the relevant prospectuses and other relevant materials when they become available as they will contain important information about the proposed Business Combination.

Investors and security holders will be able to obtain the documents filed with the SEC regarding the proposed transactions, when available, free of charge on the SEC’s website at www.sec.gov or from Portugal Telecom, Oi or CorpCo.

Forward-looking statements:  This communication contains forward-looking statements. Statements that are not historical facts, including statements regarding the beliefs and expectations of Portugal Telecom, Oi or CorpCo, business strategies, future synergies and cost savings, future costs and future liquidity, are forward-looking statements.  The words “will,” “will be,” “should,” “could,” “may,” “should be,” “could be,” “may be,” “estimates,” “has as an objective,” “targets,” “target,” “goal,” “anticipates,” “believes,” “expects,” “forecasts,” “intends,” “plans,” “predicts,” “foretells,” “projects,” “points to” and similar expressions, as they relate to Portugal Telecom, Oi or CorpCo, are intended to identify forward-looking statements and are subject to a number of risks and uncertainties. There is no guarantee that the expected events, tendencies or results will actually occur. Such statements reflect the current views of management of Portugal Telecom, Oi and CorpCo, and are subject to a number of risks and uncertainties. These statements are based on many assumptions and factors, including general economic and market conditions, industry conditions, corporate approvals, operational factors and other factors. Any changes in such assumptions or factors could cause actual results to differ materially from current expectations. All forward-looking statements attributable to Portugal Telecom, Oi, CorpCo or their affiliates, or persons acting on their behalf, are expressly qualified in their entirety by the cautionary statements set forth in this paragraph.  Undue reliance should not be placed on such statements.  Forward-looking statements speak only as of the date they are made.  Except as required under the U.S. federal

securities laws and the rules and regulations of the SEC or of regulatory authorities in other applicable jurisdictions, Portugal Telecom, Oi, CorpCo and their affiliates do not have any intention or obligation to update or to publicly announce the results of any revisions to any of the forward-looking statements to reflect actual results, future events or developments, changes in assumptions or changes in other factors affecting the forward-looking statements. You are advised, however, to consult any further disclosures Portugal Telecom, Oi or CorpCo makes on related subjects in reports and communications Portugal Telecom, Oi and CorpCo file with the SEC.

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TABLE OF CONTENTS

1.Announcement by Portugal Telecom, SGPS, S.A., dated October 8, 2014, “Material fact disclosed by Oi” regarding the resignation of the C.E.O. of Oi S.A.

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EX-1

Exhibit 1

Announcement  |  Lisbon  |  8 October 2014

Material fact disclosed by Oi

Portugal Telecom, SGPS S.A. hereby informs on the material fact disclosed by Oi, S.A. regarding the resignation of its CEO, according to the company’s announcement attached hereto.

Portugal Telecom, SGPS, SA Avenida Fontes Pereira de Melo, 40 1069-300 Lisbon Portugal Public company Share capital Euro 26,895,375 Registered in the Commercial
Registry Office of Lisbon and Corporation no. 503 215 058 Portugal Telecom is listed on the Euronext and New York Stock Exchange. Information may be accessed on the Reuters under the symbols PTC.LS and PT and on Bloomberg under the symbol PTC PL. Nuno Vieira Investor Relations Director nuno.t.vieira@telecom.pt Tel.: +351 21 500 1701 Fax: +351 21 500 0800

www.telecom.pt

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Oi S.A.

Corporate Taxpayers’ Registry (CNPJ/MF) No. 76.535.764/0001-43

Board of Trade (NIRE) No. 33.3.0029520-8

Publicly-Held Company

MATERIAL FACT

Oi S.A. (“Oi” or the “Company”, Bovespa: OIBR3, OIBR4; NYSE: OIBR and OIBR.C), in accordance with article 157, paragraph 4 of Law No. 6,404/76 and CVM Instruction No. 358/02, informs its shareholders and the market in general that Mr. Zeinal Abedin Mahomed Bava resigned his position as Chief Executive Officer of the Company on this date.

Pursuant to article 30-A of the Company’s by-laws, the Executive Officers, in a meeting held on this date, designated Mr. Bayard De Paoli Gontijo to exercise the functions relating to the position of Chief Executive Officer, together with his functions as Chief Financial Officer and Investor Relations Officer, until the Board of Directors resolves upon the appointment of a replacement for the position of Chief Executive Officer.

Rio de Janeiro, October 7, 2014.

Oi S.A.

Bayard De Paoli Gontijo

Chief Financial Officer and Investor Relations Officer

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