CNET

T-Mobile is telling Apple fans their new iPhone 6S or 6S Plus will get better 4G coverage than ever on the carrier's network. Guaranteed.

The company is so confident people using the latest smartphones will be pleased with its network, it's announced a program that lets customers painlessly cancel service if unsatisfied.

Apple's just-unveiled iPhones, along with other new devices such as Samsung's Galaxy S6, include support for radio frequencies that T-Mobile now uses on its 4G LTE network. These low-band frequencies extend the carrier's signal over greater distances and improve in-building coverage. So the company is convinced its customers will no longer be plagued by slow or spotty 4G service, and it's offering a Lifetime Coverage Guarantee for as long as they use these new phones on its network.

The offer is a signal to the wireless industry that the carrier's network is finally on par with those of rivals AT&T and Verizon, in terms of both download speeds and coverage. For more than two years, T-Mobile has been shaking up the industry, offering no-interest device financing, early upgrade programs and free international data, and eliminating service contracts.

But the company has had one big weakness compared with its two largest competitors: Its network. T-Mobile has worked quickly to close the gap, and Apple's 6S and 6S Plus are the first iPhones that can take advantage of the carrier's upgraded 4G LTE network.

"If you haven't tried our network lately," T-Mobile CEO John Legere said in a blog post Thursday, "you seriously haven't tried it." Legere said Apple's latest iPhones can tap into T-Mobile's upgrades and offer customers "a totally new experience with iPhone 6S and 6S Plus on T-Mobile."

T-Mobile

T-Mobile promises that if at any time within 30 days of signing up a customer decides to go to another carrier, it will reimburse them for any service costs already generated and completely refund the phone price. After the 30-day window, it will unlock the customer's phone so it can be used with another carrier, while still letting that person pay off the device in no-interest monthly installments, and refunding that current month's service costs. Legere said the deal is an extension of T-Mobile's Test Drive program, which lets customers try a new device for a week before signing up for service.

The new deal is an improvement over the standard 14-day return policy offered by T-Mobile and other carriers. It also eliminates a restocking fee for a returned device.

The program is available to new or existing Simple Choice customers who sign up for the Jump On Demand early upgrade program. Eligible devices are those that support what T-Mobile calls "Extended Range LTE," a fancy marketing term for the 700MHz frequency on LTE Band 12.

Simply put, such devices can take advantage of the low-frequency spectrum T-Mobile used to build its 4G LTE network. The new iPhones are the first Apple handsets to support LTE Band 12, but the new Samsung Galaxy S6 and the latest Galaxy Note also support it, and it's likely any devices hitting the market from now on will do so too.

Traditionally, T-Mobile has lacked the type of low-frequency spectrum, or licensed radio airwaves, that can carry signals over longer distances and penetrate through obstacles more easily. Instead, it's built much of its 3G and 4G data networks using higher-frequency spectrum that offers more capacity over shorter distances. Thus its coverage has largely been limited to dense urban markets, and its signals have been weak or nonexistent indoors for some customers.

Since its failed merger with AT&T in 2011, T-Mobile has been acquiring low-frequency spectrum and using it to extend the reach of its wireless network.

"We have been rolling out truckloads of new spectrum that carries our LTE signal twice as far from our towers, for a massive coverage expansion, and that works four times better in buildings," Legere said in his blog post. He said the new spectrum is available in 170 markets and covers more than half the US population. Legere said T-Mobile will cover more than 350 markets within three months.