Sprint activated 1.8 million iPhones during its fourth fiscal quarter or 2011, and some 40 percent of those activations were for new customers.

“Our strong fourth quarter performance illustrates the power of matching iconic devices like the iPhone with our simple, unlimited plans and industry-leading customer experience,” commented Sprint CEO Dan Hesse.

Sprint became the third U.S. iPhone carrier in October 2011 along with the launch of the iPhone 4S. The company used the offer of unlimited wireless data plans to help lure new customers into signing contracts, although it added data caps to its mobile hotspot offerings.

Despite the success Sprint has had with the iPhone, the company still showed a US$1.3 billion loss for the quarter. Those losses were linked in part to the cost of subsidizing iPhone sales.

The carrier added some 1.6 million new customers during the quarter, bringing its total subscriber base up to 55 million.

Sprint’s iPhone subscriber numbers, however, are still lagging behind AT&T and Verizon. AT&T reported selling 7.6 million iPhones in its last quarter, and Verizon sold 4.3 million iPhones.