Fueled by the launch of Apple’s iPhone 4S, Verizon Wireless sold more than 4.2 million iPhones in the fourth quarter last year — more than double the number of iPhones it sold in the third quarter. Verizon’s chief financial officer Fran Shammo revealed the carrier’s iPhone sales for the December quarter during a talk at a Citigroup conference in San Francisco on Wednesday. Verizon Wireless’s largest competitor, AT&T, is expected to have a record quarter as well for iPhone sales. While AT&T has not yet revealed any figures for the fourth quarter, we estimate that the company sold more than 5.5 million iPhones during its holiday quarter. The nation’s No.2 carrier announced last month that it expected record smartphone sales for the quarter, and it had already sold 6 million units between October and November alone. AT&T’s previous single-quarter sales record was 6.1 million smartphones.