SK Telecom posted a 26% drop in second-quarter net profit, as it increased spending to woo subscribers from its rivals, a Reuters report said.
SK, which controls 50.6% of the country's mobile market, earned 298 billion won ($295 million) in April-June net profit, compared with 403.3 billion won ($399 million) a year earlier.
Profits were lower than an average forecast for 376.3 billion won ($372 million) from Reuters Estimates.
South Korea is seeing an intensifying war over so-called 3G mobile services, with second-ranked KTF pushing aggressively for growth, and smaller rival LG Telecom entering the market last quarter, the Reuters report said.
The outlook remains weak with no sign of easing competition in an already saturated market, analysts said. Costs could rise further in the coming quarters as operators rush to offer products combining mobile services with landline and internet.