RPT-UPDATE 2-China Unicom in 3-yr deal for Apple's iPhone

* China Unicom in 3-yr deal to sell iPhone in China

* Unicom H1 net profit falls 45 pct, ahead of forecasts

* H1 Mobile unit's avg monthly ARPU 41.7 yuan vs 43.6 yuan

* EBITDA margins could be hurt by potential iPhone subsidies (Adds details)

By Kirby Chien and Joanne Chiu

BEIJING/HONG KONG, Aug 28 (Reuters) - Apple's iPhone will go on sale later this year in China, the world's largest mobile market, but its partner China Unicom (0762.HK) may find selling the phone carries its own burdens.

China's No. 2 mobile carrier is looking at the popular iPhone as a new gateway to profit, after posting a better-than-expected 45 percent fall in first-half profit on Friday.

Unicom's announcement on Friday ended months of rumours about a tie-up with Apple (AAPL.O), which has been trying to bring the iPhone to some of China's nearly 700 million mobile subscribers.

The company did not give a price for the iPhone, but Chairman and Chief Executive Chang Xiaobing told reporters that it would be competitive. The company said the launch is expected in the fourth quarter of 2009.

Unicom may have to offer substantial subsidies to reach a competitive price, as the deal comes just a day after rival China Telecom (0728.HK) said it would increase its budget for handset subsidies to 37 percent of wireless revenues, from 30 percent.

"Many foreign operators have seen their EBITDA margins fall after launching iPhones, said Marvin Lo of Daiwa Securities, based in Hong Kong. "So I am concerned China Unicom's margins could also come under pressure."

Unicom and rivals China Mobile (0941.HK), the world's largest mobile carrier, and China Telecom, are all under a margin squeeze as they are in the middle of a three-year $58.5 billion spending spree through 2011 to build their 3G networks.

Unicom said its first-half monthly average revenue per user (ARPU), a key indicator of profitability, for its mobile services fell to 41.7 yuan, from 43.6 yuan a year ago.

NO PRICE DETAILS

Unicom said it bought the phones in a bulk purchase from Apple, and would not use Apple's traditional revenue sharing model, but did not offer any details.

The phones would not offer a Wi-Fi function, and Unicom predicted it would eventually secure a third of China's 3G market share, but did not provide a timeframe.