US operator Sprint posted sales of 1.5 million iPhones in the first quarter of 2012, down 300,000 units from its fourth quarter, swinging to a net loss of $863 million and a diluted net loss of $.29 per share, with revenues of $7.2 billion over the first three months of the year.

The carrier nearly doubled losses year on year, with fourth-quarter losses totalling $439 million and a diluted net loss of $.15 per share. Sprint’s Q1 losses include depreciation of $543 million after shutting down the Nextel platform but saw a one-off benefit from Lightsquared, after pulling the plug on its LTE 4G contract with the struggling wireless company.

Wireless service revenues reached $7.2 billion during the quarter, a 7% increase year-over-year, driven primarily by Sprint’s postpaid ARPU growth of $4.03 – which it says is the largest year-over-year increase on record for US mobile operators.

The company saw 1.1 million new subscribers during bringing total ending subscribers to a record 56 million.

In terms of iPhone sales, Sprint lacked in comparison to its bigger rivals AT&T and Verizon. AT&T announced this week that it had activated 4.3 million iPhones with Verizon falling slightly behind with 3.2 million units. However, sales remained strong from the previous quarter, where it posted 1.8 million iPhone units and became an Apple smartphone partner for the first time to offer the iPhone 4S to customers.

Moving ahead, Sprint says its Network Vision plans remain on track, with 600 new network sites already in operation and agreements made for another 7,700. It hopes to bring 12,000 sites live by end of 2012 and finish its roll-out in 2013.

The company also expects to launch 4G LTE in Houston, Dallas, San Antonio, Atlanta, Kansas City and Baltimore by mid-2012, helping to cater for new owners of its first two 4G smartphones: the Galaxy Nexus and LG Viper 4G LTE. The operator has also announced the launch of the HTC EVO 4G LTE.