The U.S. mobile-phone market remained strong in the first half of the year, with sales for music-enabled devices doubling since last year.

Manufacturers shipped 67 million units, a decrease of less than 2 percent from the second half of last year, The NPD Group said. Sales reached nearly $4.4 billion, after rebates and promotions.

The dip was within expectations, given the second half of the year included the holiday shopping season, NPD said.

Sales of music-enabled phones rose to 10 percent of all shipments in the second quarter, compared with five percent during the same period a year ago, NPD said. The percentage of phones with Bluetooth capability also increased significantly, rising to 22 percent in the second quarter from nine percent a year ago.

Motorola continued its leadership of the U.S. market, posting twice the market share of its closest competitors, Nokia and LG Electronics. The Schaumburg, Ill., handset maker upped its share in the first six months of the year by 3 percent to 32 percent. Motorola's strong performance was due to the continued popularity of its Razr models, NPD said. Nokia and LG ended June with 16 percent of the market apiece, and No. 3 Samsung had 15 percent.