STOCKHOLM, Sweden (AP) - Nokia Corp., the world's largest mobile phone maker, expects more than half of the world's population to have a mobile phone before the end of this year, the head of the company's mobile phone unit said in an interview published Thursday.

But the development, boosted particularly by strong growth in emerging markets like Africa and China, will make it a tough challenge to maintain profitability, Kai Oistamo told Swedish news agency TT.

"That's the way it is when large parts of the growth comes from emerging markets," he said.

Oistamo said he expects three billion people to have access to a mobile phone by the end of the year, and four billion in 2010.

The Espoo-based company currently has a 36 percent global market share of sold handsets, but aims to reach 40 percent in the long term. The company recorded overall sales of euro9.9 billion (US$13.46 billion) in the first quarter, up from euro9.5 billion in the corresponding quarter a year ago.

But net sales of mobile phones fell 5 percent to euro5.6 billion (US$7.61 billion) despite a 21 percent increase in volume sales.

Nokia has operations in 130 countries and employs 68,000 people.

The world's other large mobile phone makers include Motorola  Inc., Samsung Electronics Co., Sony Corp .'s and LM Ericsson  AB's joint venture Sony Ericsson as well as LG Electronics Inc.