Because the iPhone 6S will support what the carrier has dubbed its "Extended Range LTE," a marketing term for a large part of its network coverage, or spectrum, that has been inaccessible to previous iPhone models.
Specifically, the iPhone 6S, which Apple announced on Wednesday, will be able to tap into the flavor of 700MHz network spectrum that T-Mobile provides, called Band 12. This technical change will mean that iPhone users on T-Mobile effectively "won't be handicapped anymore," Bill Menezes, a research analyst for Gartner who focuses on cellular services, told Tech Insider.
If spectrum is like the highway for delivering service, network bands are the individual lanes, explained Menezes. Last year's iPhone 6 didn't support the specific band, or lane, T-Mobile used to deliver service on its 700MHz spectrum. (AT&T, Verizon, and Sprint have offered 700MHz LTE coverage on older iPhones. Verizon started calling its 700MHz service "XLTE" last November.)
But this year, the switch is getting flipped for T-Mobile.
Extended Range LTE "massively expands coverage and works four times better within buildings," John Legere, T-Mobile's CEO, said in a promotional video Thursday. T-Mobile says that the signal can also travel twice as far from cell towers which will mean better T-Mobile service outside of cities.
25 other smartphones currently support T-Mobile's 700MHz band, or Extended Range LTE, including the Samsung Galaxy S6, Moto Nexus 6, and HTC M9.
A T-Mobile spokesperson told Tech Insider that the carrier will cover an additional 600,000 square miles of the United States with LTE service in the next three months. T-Mobile says it plans to cover 300 million people nationwide by the end of this year, a similar footprint AT&T and Verizon each claim.
The promise of better coverage isn't the only method T-Mobile is using to lure in potential iPhone 6S customers. The carrier will also pay up to $650 of other carriers' penalty fees for leaving a contract early. This week it also announced a lifetime coverage satisfaction guarantee for new iPhone 6S customers, which means it will refund up to the first full month of fees for disgruntled customers and unlock the phone to take to another carrier.