By Gerry Shih LAS VEGAS (Reuters) – LG Electronics executive Frank Lee bounded onto a Las Vegas stage this week to show off a new phone for the U.S. market, the 6-inch G-Flex, which boasts a curved screen. Two hours later, in another room at the same hotel, Huawei Technologies Richard Yu unveiled the razor-thin Ascend Mate II, bragging it had a battery life of nearly two days. There was one key difference between the two product launches at the Consumer Electronics Show: the South Korean G-Flex will be sold through three U.S. carriers – T-Mobile U.S. Inc, ATT Inc and Sprint Corp. The Chinese Ascend Mate II? In two years, Chinas three biggest handset makers – Huawei, ZTE Corp and Lenovo Group Ltd – have vaulted into the top ranks of global smartphone charts, helped in part by their huge domestic market and spurring talk of a new force in the smartphone wars.