Sprint is going above and beyond with an aggressive new promotion offering a full year of free unlimited service on up to five lines for customers who switch and bring their own device from rival carriers.

And Sprint appears to be offering its best here. The promotion is available only to T-Mobile, Verizon, and AT&T BYOD customers through June 30 but includes unlimited HD video streaming, gaming at up to 8 Mbps, unlimited 4G LTE data, and 10 GB of monthly hotspot data per line. Sprint is also waiving activation fees for the newly transferred devices, and throwing in Sprint Global Roaming for good measure. The carrier is requiring an AutoPay account, but credits will be added within two billing cycles, according to the fine print.

The year of free service is set to run through July 31, 2018, when monthly costs of $60 for the first line, $40 for the second, and $30 for lines three through five will kick in. Sprint is advertising that its offer will save a family switching from Verizon with four lines more than $2,100.

Customers switching to Sprint must own the phones they’re bringing with them. Eligible devices include the iPhone 6, 6s, and SE across carriers as well as Verizon’s iPhone 5S, 5C, and 7. Owners of Google’s Nexus 5X, 6, 6P, Pixel, and special edition Samsung Galaxy S7 and S8 can also make the jump.

The main catch here appears to be that switchers have to wait until October 1 to upgrade their device on a lease or installment plan – those who upgrade prior to that date will lose their free service.

In a Tuesday research note, MoffettNathanson analysts dubbed the promotion “arguably the most aggressive promotion in the history of the U.S. wireless industry.” But in a relatively quiet second quarter, they couldn’t help but speculate on the question of “why now?”

“One can read all kinds of things into a move as aggressive as this,” the analysts noted. “When Verizon capitulated to unlimited in Q1, investors quickly assumed (rightly, as it turned out) that Verizon must have been having a truly lousy quarter.  So what are we to assume about Sprint’s motivation in pulling the trigger on a promotion that will perhaps bring in some new subscribers before the end of the quarter… but (by definition) won’t bring in any money?”

Among the possible triggers, MoffettNathanson listed potential impacts from Comcast’s recent push into wireless, as well as the shutdown of Sprint’s RadioShack locations and a potential desire to ease churn from past promotions.

Judging by recent comments from Sprint CEO Marcelo Claure, though, it could be something else, too: the need to just get customers to try service on Sprint’s upgraded network in the first place.

“The biggest challenge that Sprint has is convincing customers to come to Sprint, because as you know, we didn't have a great network three years ago and the brand was not at its best place,” Claure said at an investor conference last month. “But what we found is as we bring customers, they come and they’re willing to stay. That’s why last year was the best churn the company has had in many years.”

The multi-line element of the latest promotion also plays into Claure’s previous comments that Sprint targets families for their lower churn profile and higher account values.

No matter what sparked the promotion, though, MoffettNathanson predicted the industry response will be swift – and harsh.