* Operating profit rises 13 pct to 1 trln yen, below estimates

* Says keen for Sprint deal with T-Mobile, open to other offers

* Says Vision fund expected to be finalised soon (Adds comments on T-Mobile deal potential, quarterly result)

By Makiko Yamazaki

TOKYO, May 10 (Reuters) - Japan's SoftBank Group Corp said it had notched up its second-best annual profit on cost cuts and a rise in subscribers at Sprint Corp, adding that it was eager to discuss potential M&A for the loss-making U.S. wireless unit.

Chief Executive Masayoshi Son also said the internet and telecoms giant company was close to launching a planned $100 billion Vision fund that aims to make it the "Berkshire Hathaway of the tech industry" as telecoms services markets mature.

Two and a half years ago, SoftBank abandoned talks to acquire rival T-Mobile US Inc for Sprint amid opposition from U.S. antitrust regulators but a potential merger is still close to Son's heart.

"Of all potential partners, T-Mobile is the one that would yield the most synergies, the most orthodox choice and we'd sincerely love to begin talks," he told a news conference, adding that the current U.S. administration is far more open to the possibility of a deal.

Since the previous talks, T-Mobile has overtaken its rival to become the No. 3 U.S. wireless carrier and SoftBank is now prepared to cede control to clinch a deal, people familiar with the matter told Reuters in February.

Son also said, however, that he was willing to discuss other possible deals for Sprint if there were better offers.

SoftBank's operating profit for the year to end-March climbed 13 percent to 1.03 trillion yen ($9 billion) on flat revenue growth.

That was below an average analyst estimate of 1.15 trillion yen from 20 analysts. SoftBank's numerous business including its own domestic telecoms unit, recently acquired UK chipmaker Arm as well as a vast array of investments in companies like China's Alibaba make estimating its earnings difficult.

For the fourth quarter, operating profit dropped 7.2 percent on unfavourable exchange rates.

SoftBank expects to invest at least $25 billion over the next five years in its tech fund, which would be one of the world's largest private equity investors. Son said that talks had already begun with about 30 companies on potential investments.

"I want to think big," he said. "The fund is designed to tap the coming gold rush era" when every industry is redefined by artificial intelligence, he added.

Asked about a possibility of investing in Toshiba Corp's flash memory chip unit, Son said SoftBank would not be a main player but flagged that Taiwan's Foxconn may be considering a bid with Apple Inc.

He added that he had been consulted by Foxconn founder Terry Gou on the matter but declined to elaborate further.

Foxconn, formally known as Hon Hai Precision Industry Co, is trying to woo Apple and other clients for a joint bid, sources have said. Gou and Son, both among Asia's richest men, have done business together for years.

Toshiba, hit by a crisis at nuclear unit Westinghouse, is selling the majority - or all - of its marquee flash-memory chip business - the world's second-biggest the second-biggest NAND chip producer - and has attracted a range of suitors.

SoftBank did not release a forecast for the current business year, saying there were too many uncertain factors. ($1 = 113.8800 yen) (Reporting by Makiko Yamazaki; Editing by Edwina Gibbs)