A study by NPD Group says that U.S. consumers purchased 28 million mobile phones in second quarter, a 13 percent decline over the same period a year ago. The firm estimates that total sales were $2.4 billion, down 2 percent year over year. NPD says that Motorola managed to maintain its lead but its unit sales share dropped 6 percent from first quarter. Motorola led the U.S. sales with 21 percent of the market, Samsung and LG both had 20 percent share and tied for second and third place, fourth place went to Nokia with 9 percent and RIM with 7 percent. Release