Verizon Wireless, the largest US mobile carrier, sold 4.2 million Apple iPhones in the fourth quarter, more than doubling from the third quarter, said Francis Shammo, finance chief of the company’s parent.

The iPhone sales will decrease gross margins by 500 to 600 basis points. A basis point is one-hundredth of a percentage point.

Shammo made his remarks yesterday at a Citigroup event in San Francisco.