Sprint (NYSE: S) is quietly testing new unlimited data plans in a handful of markets across the U.S. And it appears to have taken a page from T-Mobile's (NYSE:TMUS) playbook to do it.

Wave7 Research reported that the nation's fourth-largest operator is advertising one plan to consumers in Milwaukee and Boston that offers a first line of unlimited talk, text and data for $60 a month, a second line for $40 a month and additional lines for $25 each. A second unlimited-everything plan is available in Oklahoma and parts of Arizona for $50 each per month for the two lines and $25 per month for additional lines.

The offerings are marketed as the "Unlimited Freedom Plan." A Sprint executive declined to confirm or offer any comment on the trials, but said the carrier regularly tests a variety of new offerings both for consumers and for its business partners.

"We do trials all the time," said David Tovar, Sprint's vice president of corporate communications, in an interview with FierceWireless. "We're in the market with a number of different things at any given point in time. As a matter of practice we don't comment on those trials."

The trial deals are significantly cheaper than the unlimited plans Sprint currently offers nationwide, which include a single line for $75 a month, a second line at $45 a month and additional lines for $30 a month. And Sprint doesn't charge overages for its monthly tiered plans, but rather throttles network speeds after users have consumed their monthly data allotments.

The Unlimited Freedom Plans are also far less expensive than T-Mobile's unlimited plans, which start at $140 a month for two lines and top out at $220 for four lines. And AT&T's (NYSE: T) unlimited offering – which is available only to DirecTV subscribers – costs $100 a month for the first line and $40 a month for each additional line.

Indeed, Sprint is overtly taking direct aim at the No. 3 carrier. "Signage at Best Buy explicitly compares Sprint unlimited pricing of $70 to $95 for T-Mobile and a multi-line comparison is also provided," Wave7 wrote in a note to subscribers.

And Sprint also appears to be "optimizing" -- or degrading -- streaming data for Unlimited Freedom subscribers, just as T-Mobile does for users of its zero-rated Binge On and Music Freedom services. The strategy enables carriers to lighten the network payload even as users consume more data.

A Sprint web page touting the offerings explains that "Streaming may be optimized with video streams at up to 480p+ resolution and music streams at extreme quality (at up to 500Kbps). All while on the Sprint Network. Data deprioritization applies during times of congestion."

Tovar declined to offer a definition for "deprioritization."

Sprint could go a long way toward shoring up its customer base if it can manage to bring its Unlimited Freedom offering to market nationwide at prices that significantly under cut its competitors, of course. But whether that would be financially viable for the struggling carrier is far from clear.

For more:

- see this Sprint Unlimited Freedom Plan web page

- check this Reddit thread

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