Japan’s largest mobile phone operator NTT DoCoMo (NYSE: DCM) released its earnings for the nine months ending December 2007 today, which includes its third quarter results. From October through December, the operator’s profits climbed 38.4 percent to 130 billion yen ($1.2 billion), which it attributed to the introduction of new discount price plans launched in November that cut monthly fees by up to 44 percent, while at the same time asking users to migrate to more expensive phones (Earnings release in PDF here).

DoCoMo’s operating profit for the third quarter rose 35 percent to 216.5 billion yet ($2.03 billion), up from 160 billion yen in the same period last year, while group revenue dipped 1.4 percent to 1.197 trillion yen ($11.34 billion.)

According to Bloomberg, DoCoMo’s profit surge was the first profit in seven consecutive quarters for Japan’s largest mobile network, which said it expected the competitive environment in the Japanese mobile phone market to “remain harsh.” DoCoMo has struggled to keep subscribers amid tough competition from rival carriers KDDI and Softbank. In a bid to attract more subscribers, DoCoMo plans to launch 13 new handset models in the Spring to follow up on the success of its November roll out of FOMA handsets. While analysts noted that the price plans had a positive impact on results that would probably last through the first half of the fiscal year, slashing prices was a short term fix. Tokyo-based Diam Co. fund manager Yasuhiko Hirakawa told Bloomberg, “DoCoMo can’t rely on this alone to boost earnings in the long term.” The operator kept its annual net profit forecast for the fiscal year ending March 31 unchanged at 476 billion yen, up 4.1 percent from a year earlier.