Apple has become the leading U.S. mobile-phone vendor for the first time last quarter, securing a record 34% of market share, and knocking rival Samsung off the top spot. The Cupertino, Calif., company shipped 17.7 million phones during the fourth quarter, growing 4% annually, according to a new report by research firm Strategy Analytics. For comparison; that number jumped from 12.8 million in the fourth quarter of 2011, when Apple captured 25% of the market.