UPDATE 1-SoftBank’s mobile unit launches $21 bln IPO

* To sell shares at tentative price of 1,500 yen each

* Sale completes transformation of SoftBank into tech investor

* Unit challenged mobile duopoly, brought iPhone to Japan (Adds details of IPO, context)

TOKYO, Nov 12 (Reuters) – SoftBank Group Corp’s domestic telecoms unit on Monday received approval to list on the Tokyo Stock Exchange in an initial public offering (IPO) worth 2.4 trillion yen ($21.04 billion), a regulatory filing showed, one of the biggest IPOs ever.

The unit, SoftBank Corp, will list on the Tokyo Stock Exchange on Dec. 19, the filing with the Ministry of Finance showed on Monday.

The IPO will mark the transformation of the parent company from a mobile phone network provider – which successfully challenged Japan’s incumbent duopoly – into one of the world’s biggest technology investors under Chief Executive Masayoshi Son.

The offering will also provide the group with funds that can be redeployed into more tech investments. SoftBank’s bets have been as varied as small gaming startups, ride-hailing firms such as California-based Uber Technologies Inc, and Chinese e-commerce behemoth Alibaba Group Holding Ltd.

On sale is 1.6 billion SoftBank Corp shares at an tentative price of 1,500 yen each, raising 2.4 trillion yen and resulting in a market value of 7.18 trillion yen upon listing. The parent will retain a 66.5 percent stake in the newly listed unit.

Additionally, up to 160 million shares worth 240.6 billion yen will be offered in an overallotment if demand is strong. In that case, the total would come close to the $25 billion worth of shares sold by Alibaba in 2014 in the biggest-ever IPO.

The final IPO price will be determined on Dec. 10.

($1 = 114.0600 yen)

(Reporting by Taiga Uranaka and Sam Nussey; Editing by Christopher Cushing)