SK Telecom announced its earnings for the first quarter of 2008 - revenue of KRW 2 . 837 trillion , operating income of KRW 554 billion , and net income of KRW 382 . 9 billion .   The revenue increased by 4 . 6 % year on year while operating income and net income declined by 16 . 3 % and 3 . 4 % respectively .   Backed by the continued subscriber growth , the revenue expanded 4 . 6 % year on year . On a quarter - on - quarter basis , the revenue was reduced by 2 . 7 % due to the T - to - T Calling Plan released in October 2007 and 30 % cut in phone - mail tariff earlier this year .   As SK Telecom lowered phone - mail tariff and released “ ting ” Control Rate , a capped mobile plan for teenagers , the revenue of wireless Internet declined to KRW 597 . 3 billion , down by 11 . 8 % year on year and 17 . 3 % quarter on quarter .   With competition in the WCDMA market heating up , the marketing expenses increased 30 . 7 % year on year . However , due to efficient marketing expense management the expenses went down from the previous quarter to KRW 766 . 8 billion , posting a 10 . 2 % decrease . The marketing expenses accounted for 27 % of the total revenue .   Due to the reduced marketing expenses , the operating income rose to KRW 554 billion , grown by 78 . 3 % from the previous quarter . Compared to the previous year , however , the operating income decreased by 16 . 3 %.   The 2008 1 Q cumulative subscriber count is 22 . 37 million , gained 8 % year on year . Average revenue per user ( ARPU ) decreased to KRW 42 , 654 , down by 3 % year on year because of phone - mail tariff cut and T - to - T Calling Plan . [ 관련 기사 ] ☞ SKT , 1 분기 매출 2 조 8370 억 원 … 전 분기 대비 2 . 7 %↓< 저작권자 ⓒ 디지털 데일리 무단 전재 - 재 배포 금지 >