ZURICH, June 30 (Reuters) - Switzerland"s no.3 telecoms group Salt is preparing for a Zurich stock market flotation in the autumn in a deal that could value the company at about 2.5 billion Swiss francs ($2.7 bln), three people close to the matter said. French entrepreneur Xavier Niel is seeking an exit after seven years of investment, they added. The company is expected to sell shares worth roughly 700 million Swiss francs ($757 million), mainly new shares from a capital increase, the people said. Credit Suisse (CSGN.S), Goldman Sachs (GS.N), Morgan Stanley (MS.N) and BNP Paribas (BNPP.PA) are organising the flotation, they added. Salt said that the company and its owner are considering financing options, including an IPO, adding that no decisions have been taken. The banks declined to comment or were not immediately available for comment. Salt last year posted adjusted earnings before interest, tax, depreciation and amortisation of 421 million francs on revenues of 1 billion francs. In the first quarter, core earnings were down 3%, while sales were up 2.5%. Swisscom (SCMN.S) trades at about 8 times its expected core earnings, and a person familiar with the matter said that Salt, which competes mainly over price, should brace for a valuation discount of 20-25% compared to the incumbent. The IPO could value Salt at roughly 2.5 billion francs, including debt, the people said. Salt, formerly Orange Communications, was bought by Niel from buyout firm Apax in 2014 for 2.8 billion Swiss francs. The telecoms entrepreneur has, however, since benefited from dividend payments and streamlined the business through deals like Salt"s sale of its telecoms towers to Cellnex. Switzerland"s telecommunications sector has consolidated in recent years and Liberty Global"s (LBTYA.O) 6.8 billion Swiss franc takeover of Sunrise Communications closed in late 2020, reducing the number of large players to 3 from 4. Earlier this year, Salt struck a fibre-optic partnership with Swisscom, which will enable Salt to provide fiber-to-the-home connections to 3 million customers by 2025. ($1 = 0.9241 Swiss francs)