China Mobile, the world's biggest mobile operator by subscribers, said Wednesday net profit rose 3.9 percent last year on rapid growth in added services such as music downloads.

The company posted a full-year net profit of 119.6 billion yuan ($18.1 billion), compared with 115.1 billion yuan in 2009, according to a statement filed with the Hong Kong Stock Exchange.

China Mobile said it added 61.7 million new customers last year for a total of 584 million accounts, but most of the new clients came from the rural and migrant markets, which meant they are likely to spend less than urban users.

The company, which competes with rival China Unicom and China Telecom, said its average revenue per user -- a key telecoms industry barometer to measure long-term growth rates, fell to 73 yuan last year from 77 yuan in 2009.

"Increasing mobile penetration in China will further intensify competition in the telecommunications industry," the company said in the statement.

Its fast-growing "value-added" services, including games, music downloads and payment systems, helped drive growth -- accounting for 31.2 percent of total operating revenue.

China Mobile, which operates a 3G mobile network based on the home-grown TD-SCDMA standards, said it had 20.7 million 3G users at the end of 2010.

The company is also carrying out testing of the homegrown candidate for the 4G standard, known as TD-LTE, in seven cities including Beijing.

It plans to increase capital expenditure this year to 132.4 billion yuan with 53 percent of the budget spent on network infrastructure, compared with 124.3 billion yuan in 2010, the statement said.

The company said in a separate statement Wednesday that its China Mobile Communication unit had agreed to buy China Topssion Communication Co, which sells mobile phones and other devices, for 237.1 million yuan.

Huawei and ZTE, China's leading telecom equipment makers, currently own 16 percent and 10 percent of Topssion respectively.

Before the results were released, Hong Kong-listed shares of China Mobile closed down 1.73 percent at HK$71 ($9.10), underperforming the benchmark Hang Seng Index, which edged up 0.10 percent.