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Filed by Portugal Telecom, SGPS, S.A.

pursuant to Rules 425 and 163 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 capital increase and related public offering of common shares and preferred shares by Oi S.A. (“Oi”), (2) the proposed merger of shares (incorporação de ações) between Telemar Participações S.A. (“TPart”) or another company identified for this purpose (“CorpCo”), on the one hand, and Oi, on the other hand, and (3) the proposed merger (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”).

Oi may file a registration statement (including a prospectus) with the U.S. Securities and Exchange Commission (the “SEC”) for the offering of its common shares and preferred shares to be issued in connection with its proposed capital increase. Before you invest, you should read the prospectus in that registration statement and other documents Oi has filed with the SEC for more complete information about Oi and this offering. You may get these documents for free by visiting EDGAR on the SEC Web site at www.sec.gov. Alternatively, Oi will arrange to send you the prospectus after filing if you request it by calling toll-free 1-855-672-2332.

In connection with the proposed merger of shares between CorpCo and Oi and the proposed merger of Portugal Telecom with and into CorpCo, CorpCo or one of its affiliates plans to 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 mergers, when available, free of charge on the SEC’s website at www.sec.gov or from Portugal Telecom, Oi or TPart. This communication contains forward-looking statements. Statements that are not historical facts, including statements regarding the beliefs and expectations of Portugal Telecom, Oi, TPart, business strategies, future synergies and cost savings, future costs and future liquidity, are forward-looking statements.  The words “will,” “may,” “should,” “could,” “anticipates,” “intends,” “believes,” “estimates,” “expects,” “plans,” “target,” “goal” and similar expressions, as they relate to Portugal Telecom, Oi, TPart, 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 TPart, and are subject to a number of risks and uncertainties. These statements are based on many

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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, TPart 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, TPart 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 TPart makes on related subjects in reports and communications Portugal Telecom, Oi and TPart file with the SEC.

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Announcement | Lisbon | 2 October 2013

PT and Oi announce a combination of their businesses

www.telecom.pt

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PT announced today that it has entered into a memorandum of understanding with Oi, AG Tel, Bratel Brasil S.A. (“Bratel”), Pasa Participações S.A. (“Pasa”), LF Tel, EDSP 75 Participações S.A. (“EDSP75”) (which together with Tpart are defined as “Oi Holding Companies”), BES and Ongoing setting out the basis for a proposed merger (the “Business Combination”) between the PT and Oi groups and the Oi Holding Companies to be combined into a single entity, Tpart or a new company to be created for this purpose (in either case, “CorpCo”).

Creation of a leading telecoms operator

The merger is the natural fulfilment of the industrial alliance established in 2010 between PT and Oi. The combination of PT and Oi will create a leading telecoms operator with operations covering a population of c. 260 million people and c. 100 million subscribers. The merger will consolidate the position of both companies as the leading operator for Portuguese-speaking countries with leadership positions in all markets where it operates. The combined company will aim to achieve significant economies of scale, maximise operational synergies and add value for its shareholders, customers and employees.

CorpCo will operate in strategic markets and benefit from compelling growth prospects in Brazil and mature operations in Portugal geared for economic recovery.

The Business Combination will enhance the implementation of strategic initiatives already underway, where PT and Oi have been sharing expertise and know-how in areas such as product development, customer care, engineering, operations and IT.

Commitment to highest corporate governance standards

As part of the merger, CorpCo intends to be listed on the Novo Mercado segment of BM&FBovespa, on the NYSE Euronext and on the NYSE, and implement best-in-class corporate governance with one class of shares with equal voting and dividend rights for all shareholders.

The Board of Directors for the first three-year term of office will be composed by the following members: Alexandre Jereissati Legey, Amilcar Morais Pires, Fernando Magalhães Portella, Fernando Marques dos Santos, Henrique Manuel Fusco Granadeiro, José Maria Ricciardi, José Mauro Mettrau Carneiro da Cunha, Nuno Rocha dos Santos de Almeida e Vasconcellos, Rafael Luís Mora Funes, Renato Torres de Faria e Sergio Franklin Quintella. José Mauro Mettrau Carneiro da Cunha and Henrique Manuel Fusco Granadeiro will be Chairman and Vice-Chairman of the Board of Directors, respectively.

Unified management team led by Zeinal Bava

Zeinal Bava, CEO of Portugal Telecom from 2008 to 2013 and the current CEO of Oi and PT Portugal, will be the CEO of CorpCo and its subsidiaries.

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Improved time to market to crystalise growth opportunities in Brazil

The proposed merger will allow CorpCo to leverage Oi’s unique footprint in Brazil and PT’s experience in the Portuguese market, thus allowing it to crystalise the growth opportunities in convergence and mobility in Brazil.

Commitment to financial discipline and value creation

The combined entity will focus on achieving operational excellence. A clear action plan has been prepared aiming at integrating areas yielding incremental efficiencies, including the appointment of teams to monetise synergies and address existing operational challenges.

The Business Combination is expected to generate synergies estimated to have a NPV of R$ 5.5 billion (Euro 1.8 billion).

CorpCo is committed to strengthen further its financial discipline to improve the cash-flow profile to underpin investment in future growth areas and balance sheet flexibility.

Capital increase at Oi

Oi proposes to undertake a capital increase to be subscribed in cash and in kind (the “Oi Capital Increase”).

Oi targets to raise R$ 8.0 billion (Euro 2.7 billion), with a minimum of R$ 7.0 billion (Euro 2.3 billion), in cash (the “Cash Capital Increase”), to improve the balance sheet flexibility of CorpCo.

Shareholders of Tpart and an investment vehicle managed by BTG Pactual will subscribe approximately R$ 2.0 billion (Euro 0.7 billion) of the Cash Capital Increase.

In addition and subject to the Cash Capital Increase, PT will subscribe to a capital increase in kind of approximately R$ 6.1 billion (Euro 2.0 billion) (“Capital Increase in Kind”) fully subscribed through with the contribution of the PT Assets (as defined below).

The Oi Capital Increase of R$ 14.1 billion (Euro 4.7 billion) will be executed through the public issuance of common shares and preferred shares of Oi, in proportion to the current ratio between the common and preferred shares of Oi issued and outstanding.

The “PT Assets” shall be composed of all the shares directly or indirectly held by PT in companies that hold (i) all of its operating assets, excluding those directly or indirectly held in Oi and Contax Participações S.A. (“Contax”), and (ii) the respective liabilities as of the date of contribution. The PT Assets will be subject to a valuation by an

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independent appraiser, whose report shall be submitted to Oi’s Shareholders General Meeting. PT’s participation in the capital increase will also be subject to approval by PT’s Shareholders General Meeting.

Without prejudice to the valuation report of the PT Assets referred to above, PT estimated the equity value of PT Assets to be Euro 2.0 billion (equivalent to R$ 6.1 billion), within a range of a minimum of Euro 1.9 billion and a maximum of Euro 2.1 billion, equivalent to R$ 5.8 billion and R$ 6.4 billion, respectively, based on the exchange rate of Euro to Brazilian real of 3.0181. PT may elect not to consummate the subscription of shares in Oi Capital Increase in the event that the valuation report referred to above concludes that the value in Euro ascribed to the PT Assets is less than the estimated amounts indicated above, based on the exchange rate of Euro to Brazilian Real on the business day immediately prior of the issuance of the report.

The Oi Capital Increase is conditional to the full subscription of a minimum of R$ 7.0 billion (Euro 2.3 billion) of the Cash Capital Increase. The other conditions of the Oi Capital Increase will be set forth in the definitive agreements that will govern the Business Combination and will be disclosed at the appropriate time to our shareholders and the market in general.

At completion, post the incorporation of Oi shares into CorpCo, and assuming the targeted cash capital increase of R$ 8 billion (Euro 2.7 billion) at Oi’s last 30 calendar days VWAP (R$ 4.36 or Euro 1.45 per share), the PT shareholders will own 38.1% of the voting and outstanding capital of CorpCo.

PT may elect not to subscribe the Oi Capital Increase if the percentage participation of the PT shareholders in CorpCo after the Oi Capital Increase is equal to or less than 36.6% of the total capital of CorpCo on a fully diluted basis pro forma to the incorporation of Oi shares by CorpCo. Additionally, Tpart will not be obligated to consummate the Business Combination if the percentage participation of the PT shareholders in CorpCo after the Oi Capital Increase is greater than 39.6% of total capital of the CorpCo on a fully diluted basis pro forma to the incorporation of Oi shares by CorpCo.

Business Combination Steps

All steps prior to the final merger of PT into CorpCo are inter-conditional. The steps described below are illustrative, and a comprehensive description of all corporate actions to be undertaken will be disclosed at the appropriate time and will be included in the documentation to be submitted to the approval by shareholders.

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Based on the estimated value for the PT Assets as mentioned above, it is anticipated that in exchange for each PT share, shareholders will receive the equivalent of Euro 2.2911 in CorpCo shares (to be issued at the price of Oi’s share capital increase) plus 0.6330 shares in CorpCo.

Upon completion, CorpCo shares will be listed on the Novo Mercado segment of BM&FBOVESPA, on the NYSE Euronext and on the NYSE.

Conditions to closing

The consummation of the Business Combination will be subject to the following conditions:

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The MOU expires on 1 October 2014 and may be extended by the parties

Contacts:

Luís Pacheco de Melo (Chief Financial Officer)

Nuno Vieira (Investor Relations Director)

nuno.t.vieira@telecom.pt

Tel.: +351 21 500 1701

Fax: +351 21 500 0800

Important Notice:

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, and does not constitute an offer, solicitation or sale in any jurisdiction in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of that jurisdiction.  Investors in shares or American Depositary Shares of PT or Oi and U.S. holders of shares of PT and Oi are urged to read the U.S. prospectus(es) regarding the Business Combination, when they become available, because they will contain important information.  The U.S. prospectus(es) will be filed with the SEC as part of a Registration Statement on Form F-4 of CorpCo or one of its affiliates.  Investors and security holders may obtain a free copy of the U.S. prospectus(es) (when available) and other documents filed by PT, Oi and, if applicable, CorpCo with the SEC at the SEC’s website at www.sec.gov. A copy of the U.S. prospectus(es) (when available) may also be obtained for free from PT or Oi.

Oi may file a registration statement (including a prospectus) with the U.S. Securities and Exchange Commission (the “SEC”) for the offering of its common shares and preferred shares to be issued in connection with its proposed capital increase. Before you invest, you should read the prospectus in that registration statement and other documents Oi has filed with the SEC for more complete information about Oi and this offering. You may get these documents for free by visiting EDGAR on the SEC Web site at www.sec.gov. Alternatively, Oi will arrange to send you the prospectus after filing if you request it by calling toll-free 1-855-672-2332.

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Forward-Looking Statements:

This communication contains forward-looking statements. These statements are statements that are not historical facts, including statements regarding the outlook and expectations of PT, Oi and CorpCo, business strategies, future synergies and cost savings, future costs and future liquidity.  The words “expects,” “believes,” “estimates,” “plans,” “anticipates,” “may,” “will,” “should,” “could,” “target,” “goal” and similar expressions, when used in relation to PT, Oi and CorpCo, are intended to indicate forward-looking statements.  These statements reflect the current outlook of the management of PT, Oi and CorpCo and are subject to a number of risks and uncertainties.  There is no guarantee that the expected events, trends or results will actually occur. The statements are based on many assumptions and factors, including general economic and market conditions, industry conditions, operational factors, corporate approvals 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 us, or persons acting on our behalf, are expressly qualified in their entirety by the cautionary statements set forth in this paragraph.  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, we 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 PT, Oi or CorpCo makes on related subjects in reports and communications PT, Oi and CorpCo file with the SEC.