Sprint has posted its fourth quarter financial report, announcing a hefty $1.3 billion net loss, only to increase its operating revenues by the largest amount in five years to $8.72 billion.

With net subscribers hitting 55 million (33 million postpaid, 14.8 million prepaid and 7.2 million from wholesale), the company added an extra 1.6 million subscribers in its first quarter, helped by strong iPhone sales.

With Sprint finally offering its first Apple device with the launch of the iPhone 4S, the third biggest US carrier sold 1.8 million iPhone handsets, 40% of which went to new subscribers. In comparison, Verizon Wireless sold 4.3 million iPhones in the last quarter and AT&T activated 7.6 million of the devices.

With figures now available from the top three mobile operators in the US, it allows us to see how AT&T, Verizon and Sprint affected worldwide iPhone sales. Between them, they sold 13.7 million iPhones, meaning that the US accounted for 36.9% (rounded to 37%) of Apple’s 37.04 million iPhone sales during its first fiscal quarter.

US mobile operator AT&T announced its fourth quarter financial results in January, declaring that it saw huge growth in mobile broadband sales and smartphone activations, with the iPhone accounting for 81% of all smartphones activated by the carrier.

AT&T activated 9.4 million smartphones in its last quarter, with Apple’s iPhone contributing 7.6 million of the activations. Despite the huge growth of Apple activations, it was also a record quarter for Android activations.

In comparison, Verizon activated 2.3 million 4G devices and 4.3 million iPhones, doubling from the third quarter’s 2 million, but even then AT&T still sold 77% more iPhones than Verizon in the last quarter.

All three carriers have reported losses based on the multi-year contracts they offer with the iPhone 4S in order to increase subscriptions. With two-year contracts proving popular, they might have to wait until 2014 until figures reflect these impressive iPhone sales.