added info: the age structure of Korea might help explain the numbers:
0-14 years: 18.9% (male 4,844,083/female 4,368,139)
15-64 years: 71.9% (male 17,886,148/female 17,250,862)
65 years and over: 9.2% (male 1,818,677/female 2,678,914) (2006 est.)
[CIA - The World Factbook]
Number of mobile phone users in S. Korea tops 40 mln
(Yonhap) -- The number of mobile phone users in South Korea has exceeded a record 40 million for the first time, industry sources said Sunday.
SK Telecom Co., KTF and LG Telecom Ltd. said that as of Friday they had slightly more than 40.01 million people in the country with registered mobile phones. This number was reached 22 years after analogue-type mobile phone service was first introduced in 1984 and 10 years after the country switched to the code division multiple access (CDMA) system.