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UPDATE 1-Japanese telco SoftBank posts 15% rise in Q3 profit, hikes full-year forecast

forecast@

* Operating profit Y243 bln vs Y240 bln estimate of analysts

* Upgrades full-year profit forecast to Y900 bln from Y890 bln

* Parent SoftBank Group reports its earnings on Wednesday (Adds forecast upgrade, context)

TOKYO, Feb 7 (Reuters) - Japanese telco SoftBank Corp on Friday reported a 15% rise in third-quarter operating profit, beating estimates, underpinned by its mobile business.

SoftBank also raised its full-year operating profit forecast to 900 billion yen ($8.19 billion) from 890 billion yen previously.

Operating profit in the October-December quarter was 243 billion yen versus 211 billion yen a year earlier. That compared with an average forecast of 240 billion yen from three analyst estimates compiled by Refinitiv.

Japan's third-largest telco, SoftBank Corp has pledged to pay out 85% of its net income as dividends, providing a steady stream of cash to tech conglomerate SoftBank Group Corp , which holds a 67% stake.

Along with a 26% stake in China's Alibaba, the wireless carrier continues to help prop up the market value of its parent, which in the quarter ended September reported its first quarterly loss in 14 years as its tech bets faltered.

Founder Masayoshi Son built his fortune by breaking into Japan's telecoms market but his reputation could be determined by the performance of the $100 billion Vision Fund, which will report at the group's results on Wednesday.

SoftBank Corp rivals NTT Docomo and KDDI Corp reported last week that operating profit fell 15% and rose 11%, respectively.

SoftBank's stable earnings contrast with the fortunes of one of Son's big early overseas bets, U.S wireless unit Sprint Corp , which last week reported falling subscriber numbers.

Analysts said prospects for the money-losing telco are grim if it does not reach a merger with larger rival T-Mobile US Inc .

Japan's three incumbent telcos are holding their breath for the announcement of pricing plans from Rakuten Inc, which will launch wireless services in April and is expected to offer aggressively low prices. ($1 = 109.8700 yen)

(Reporting by Sam Nussey; Editing by Christopher Cushing)