Sprint wants to reward its existing customer base for its loyalty.

Apple

The company said on Tuesday that it is offering a "Loyalty Service Credit" of $15 to Sprint customers looking to lease Apple's new iPhone 6 or iPhone 6 Plus . When applied to the lease cost of $20 for an iPhone 6, the monthly fee comes out to $5 a month. An iPhone 6 Plus will cost $10 a month.

The loyalty program is the latest move by Sprint to turn its slumping subscriber base around. The company previously announced individual and family plans that undercut the competition -- or at least offered more data -- and last month introduced its $50 unlimited plan specifically for the iPhone. That plan comes with a $20 monthly fee for leasing a new iPhone 6 or iPhone 6 Plus, in which the customer would hand back the device to Sprint after two years.

The knock on Sprint's plans is that they were largely designed to snare new customers, leaving its existing base without any real benefits. The "Loyalty Service Credit" rewards existing customers who have stuck with the struggling carrier.

Customers can keep their existing smartphone plans, no matter the configuration, and can take advantage of the credit as long as they sign up to lease a new iPhone 6 or iPhone 6 Plus. Customers will continue to get the credit as long as they have an active lease and remain on a qualifying plan.

The promotion lasts from October 13 to January 15.

At the end of 24 months, customers can turn in the iPhone 6 for another iPhone, purchase the device, continue leasing it on a month-to-month basis or turn it back in and terminate the service.

Sprint has shown new life under new CEO Marcelo Claure, who is attempting to take some of the spotlight away from T-Mobile's firebrand CEO John Legere, who over the last year successfully managed his own turnaround of a struggling business. Legere likewise used a combination of savvy promotions, improvements in T-Mobile's network and a bit of hype to garner attention and interest.

While Sprint has been aggressive with its plans, its network coverage continues to lag behind its competitors due to the complicated process of upgrading its equipment. The company risks attracting new users, only to turn them off if the service is inadequate. The company has managed to cover some of the bigger cities with LTE, but its reach still falls far behind the other three carriers.