On the heels of Apple's big event last week, T-Mobile (NASDAQ:TMUS) CEO John Legere recently took to his video blog to promote the carrier's new Lifetime Coverage Guarantee.  The offer is aimed directly at new iPhone 6s and 6s Plus users, and T-Mobile's hoping it can show off its new spectrum strength to its network doubters. 

The Lifetime Coverage Guarantee is for new or existing Simple Choice customers -- who are signed up for T-Mobile's JUMP! On Demand phone upgrade plan -- and if customers aren't satisfied with their wireless coverage within the first 30 days, they can return their smartphone and get a full refund of up to one month's service.

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Source: T-Mobile.

Specifally, T-Mobile will pay:

  • The monthly service charge, taxes, and fees
  • SIM card starter kit (and won't charge you a restocking fee)

And if you use the phone beyond 30 days, you can still take advantage of the offer. T-Mobile says, "Additionally, beyond 30 days, you can cancel your service at any time, received up to full month of service refund, have your iPhone unlocked and even keep your interest free financing plan."Customers just have to call T-Mobile or visit a store before to enact the Lifetime Coverage Guarantee, or the carrier won't honor it. "

All JUMP! On Demand phones with Extended Range LTE are included in the guarantee and, in theory, that should mean Samsung's Galaxy S6, S6 Edge, Note 5 and a few others will make the cut, but T-Mobile hasn't spelled out which phones are on the list yet.

Why do this?
T-Mobile's trying to showcase its Extended Range LTE, but it's more commonly known in the wireless industry as 700MHz spectrum, or Band 12. Don't let your eyes glaze over on this just yet. T-Mobile says this type of spectrum offers up better signal coverage inside of buildings and allows the same LTE signals to travel twice as far from some towers.

And it's the reason why T-Mobile's new guarantee is timed with the new iPhone 6s and 6s Plus. Both of the devices now have LTE bands capable of handling 700 MHz signals. Legere said on his vlog:

Apple's latest iPhones can tap into all that T-Mobile coverage because -- for the first time ever -- iPhones come with T-Mobile Extended Range LTE support built in! That means a totally new experience with iPhone 6s and 6s Plus on T-Mobile.

Right now, the Un-Carrier has 700 MHz deployed in 170 markets across the U.S. -- which it says covers half of the population -- but that will bump up to 350 markets over the next three months. 

T-Mobile's strategy
As more phones with 700 MHz capabilities hit the shelves, T-Mobile customers could see a bit of improvement on their devices, though it's hard to measure how much. But any incremental improvement would be a good one.

While T-Mobile's been great at getting new customers to sign up for its service, and has added 2.1 million branded customers in the first half of the year,  its network still falls behind Verizon, AT&T, and Sprint. Despite it's rapid rollout of its LTE network, and technically having the fastest LTE network, T-Mobile fails to outpace the competition in overall network performance. But with more and more devices now using 700 MHz spectrum, that may soon change.

It's hard to quantify how the Lifetime Coverage Guarantee will improve T-Mobile subscriber numbers, but with the carrier expected to add 3.4 million to 3.9 million new branded subscribers this year, it's clear T-Mobile's previous promotions have succeeded in attracting new users. Hopefully, with the carrier's 700 MHz spectrum now being put to good use, it'll be able to convince them that its network is indeed getting stronger.

Chris Neiger has no position in any stocks mentioned. The Motley Fool owns and recommends Apple, and recommends Verizon Communications. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.