Earlier this month we brought you news that Sprint had unveiled a new Android smartphone – the LG Viper – that would be available on the company’s fledgling 4G LTE network when it launched. While the phone itself was not especially remarkable, one part of the announcement was pretty important: it hinted that Sprint would continue offering its unlimited data plans once the transition to 4G LTE was made.

Today, Sprint confirmed that customers on their 4G LTE network will indeed have the option of an unlimited data plan. When asked whether Sprint would continue the practice of offering unlimited 4G data plans, Sprint CEO Dan Hesse told CNet that he was “not anticipating the unlimited plan would change by [the iPhone launch].”

Sprint’s unlimited data plan is, as Hesse said, the carrier’s “distinctive differentiator.” Sprint is the only carrier that still offers unlimited data to smartphone users. While AT&T and Verizon both offered such plans when the iPhone launched on their network, the plans were eventually abandoned in favor of a tiered data plan structure. Those who originally signed up for the unlimited plans have been allowed to keep them, though AT&T is in the habit of throttling the connection speeds of customers foolish enough to think unlimited actually means “unlimited.”

The fact that Sprint still offers unlimited 3G plans already makes them exceptional. The fact that they will continue to do so once their 4G network is in place makes them all the more so. Despite the fact that 4G LTE networks are able to handle larger traffic loads than 3G networks, AT&T and Verizon have made no move to offer their customers unlimited plans.

Sprint, however, needs the iPhone very badly. As we reported this morning, the company posted a net loss of $255 million in the first quarter. The iPhone, however, went a long way toward keeping the company afloat. During the first quarter Sprint reported a net gain of 1.1 million subscribers. They also sold 1.5 million iPhones. The company bet a lot on the iPhone when it launched on their network last year. So far – despite losses incurred by the looming shutdown of the old Nextel network – the iPhone is one of the main things keeping the carrier afloat.