Sprint is bringing a new low to the unlimited data plan. And in this competitive market, that's saying something. 

The nation's fourth-largest wireless carrier, which has a deal to merge with No. 3 T-Mobile later this year, on Thursday introduced a new unlimited data plan for $15 a month per line. The limited promotion, which is only available online or by phone, kicks off on Friday and lasts for an unspecified limited time. Allan Samson, senior vice president of acquisition for Sprint, said in an interview that this would "last weeks, not months." 

The $15 price is the cheapest offer for an unlimited data plan, undercutting even the low-cost prepaid carriers and underscoring Sprint's aggressive push to lure you in. While competition among the carriers remains fierce, the lack of new significant promotions over the last few months suggested a return to normalcy. But Sprint, under new CEO Michel Combes, looks to be stirring things up again. 

Samson acknowledged this wouldn't work financially if offered as a regular plan, and said the low price was designed to nudge people who have hesitated to switch to Sprint. This is less an engine for customer growth and more a way to build word-of-mouth buzz for Sprint. 

"There is an audience out there waiting for a reason to give Sprint a try," Samson said. "We believe this is a compelling reason." 

The unlimited data plan limits you to DVD-quality video, so you won't be able to access high-resolution Netflix shows on your phone. Sprint also has the right to throttle you to lower speeds if you're in an area with lots of traffic congestion. 

Sprint still offers its promotion for a free year of unlimited data, but the plan jumps to $60 after 12 months. Its Sprint "Unlimited Freedom," available online and in stores, costs $60 a month and includes free Hulu and high-definition video. This new plan doesn't include any of the perks, but won't include a price hike either.

Sprint has had to be more aggressive than its competitors because it continues to fight the perception that its network lags behind the other three national carriers in coverage and speed. While Sprint has made great strides in improving its service, there are still areas where it falls short of the competition. 

Sprint is among the big carriers touting a move to 5G next year. Samson said customers on this plan would still pay $15 if they purchased their own 5G phone. 

'Hello, humans': Google's Duplex could make Assistant the most lifelike AI yet.

CNET Magazine: Check out a sample of the stories in CNET's newsstand edition.