South Korean mobile phone giants Samsung Electronics Co. and LG Electronics Inc. retained their leading positions in the North American market for a 12th straight quarter in the April-June period, an industry report showed Friday. Samsung, the world\'s second-largest cellphone maker, sold 13.8 million units of mobile devices in the United States and Canada in the second quarter, extending its dominance for 12 straight quarters, according to the report by market research firm Strategy Analytics.