Sprint will continue to offer a free year of unlimited service to customers who switch to the carrier and bring their own phone. The offer was set to expire last month, but Sprint has extended the offer through April.

The offer has been available since June of 2017. It's available to new customers who switch to Sprint and sign up on the company's website. Sprint and other carriers routinely describe promotional offerings as “available for a limited time,” only to extend the offering as its end date nears.

Sprint’s promotion—which gives a free year of unlimited service to anyone who owns any one of roughly three dozen phones, including those from Apple, Samsung, Motorola, Google and others—was described in 2017 by Wall Street analyst Craig Moffett as the “most aggressive promotion in the history of the U.S. wireless industry.” (After their free year of service is over, Sprint customers must then pay $60 per month for their first line of service, $40 per month for their second line of service, and $30 per month for lines 3-5.)

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Sprint’s offer did appear to boost Sprint’s quarterly results last year—shortly after launching the promotion, Sprint posted its first quarterly profit in three years and added 88,000 net postpaid subscribers.

And in its most recent quarter, Sprint reported postpaid phone customer additions of 184,000, a figure that garnered largely positive reactions from Wall Street analysts. “While we understand the weaker phone additions, we do not believe it is overly surprising given the competitiveness the last three weeks of December,” wrote Jennifer Fritzsche of Wells Fargo in a note to investors immediately following the release of Sprint’s fourth quarter 2017 results.

But the analysts at MoffettNathanson recently warned that Sprint now faces a troubling 2018, despite the carrier’s continued offer of a free year of service. “When will Sprint run out of cash?” the analysts wondered in a recent report on the wireless sector, noting that Sprint faces, among other problems, the fact that it faces significant debt maturities over the next two years.

“Sprint doesn’t appear to be sustainable,” the MoffettNathanson analysts concluded.

For its part, Sprint has pegged much of its future on a renewed push to improve its network largely through adding 2.5 GHz capabilities to the half of its nationwide towers that don’t currently support that band, and to use that effort to roll out a nationwide mobile 5G network in the first half of 2019.