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1989-07-25
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1996-01-02
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1960-10-04
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1981-07-07
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1975-02-11
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1940-09-03
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1996-07-17
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중계회선 시스템에서 착신측 교환기로부터 전송되는비과금 안내를 구분하는 방법 및 이를 이용한 가상 번호통화연결음 서비스 방법