Portugal Telecom and Brazil's biggest telecommunications operator Oi, in which PT is the major shareholder, announced plans on Wednesday to merge into a Brazilian-registered holding company.
A PT statement said they had signed a memorandum of understanding setting out the basis of the merger which it called a "natural fulfilment of the industrial alliance established in 2010 creating a leading telecoms operator."
The merger will create a company that generates over 12 billion euros ($16 billion) in annual sales, according to pro forma 2012 results.
Shares in PT soared more than 15 percent on the announcement of the merger, which PT said would produce synergies of 1.8 billion euros ($2.4 billion).
The merger will be conducted by Oi undertaking a capital increase targeted at 2.7 billion euros, and then Oi and PT shares then being exchanged for those of the new holding company CorpCo, which will be quoted in Lisbon, Sao Paulo and New York.
Thanks to the multiple listings CorpCo "will enjoy higher liquidity and a diversified shareholder base", and they will also "underpin the highest standard of corporate governance."
Shareholders in PT, which currently owns 23.6 percent of Oi, will end up with roughly 38 percent of CorpCo depending on the size and price of the capital increase.
PT bought a 22.3 percent stake in Oi in 2010 for 3.5 billion euros.