Iphone
Source: Apple

The new Apple(NASDAQ:AAPL)iPhone 6s and 6s Plus are just about to hit store shelves. and already the devices appear to be a major success for T-Mobile(NASDAQ:TMUS). The carrier's infamously outspoken CEO, John Legere, sent out a tweet earlier this week saying that iPhone 6s pre-orders are up 30% over the iPhone 6 pre-orders from last year.

Apple, of course, deserves at least partial credit here. Apple's latest devices come with new features, like Live Photos -- short video clips taken each time you snap a picture -- a new 12 megapixel rear-facing camera, and a pressure-sensitive 3D Touch display.

But T-Mobile's also made its network more alluring by piling on the offers for new and existing subscribers. Take for example the carrier's latest iPhone offer: Current iPhone 6 users can trade in their device and pay as little as $5 per month for an iPhone 6s. And if people don't have a new iPhone to trade in, they can still get a great deal on Apple's new devices by trading in some other top-of-the-line phones as well. 

T Mobile Plans Iphone
Source: T-Mobile

What's interesting is that Legere's tweet came a day before the new On Demand iPhone 6s pricing was revealed, which means that the 30% jump in iPhone pre-orders doesn't even factor in this new plan. 

Part the early success may have come from the carrier's new Lifetime Coverage Guarantee, which the company announced the same day the iPhone 6s debuted. The plan allows new customers who sign up for a new iPhone (or any Extended Range LTE device) to try out the network virtually risk free. If users don't like T-Mobile after 30 days they can turn their device in, pay nothing for it, and receive a refund for one month of their T-Mobile service.

Building on past success
Two years ago, T-Mobile introduced its iPhone Test Drive, which allowed customer to test out the iPhone 5s on its network and turn it back in if they weren't completely satisfied. Shortly after it launched, Legere said on T-Mobile's third quarter 2014 earnings call that the carrier wouldn't stop there: 

We're looking at ways over time to expand the program. We'd like to see the whole industry create a process where people can test drive. So from that standpoint, it's a long journey, one that we're very patient with and one that we'll stick with.

And as the carrier's new JUMP On Demand pricing for the new iPhones proves, Legere meant what he said. But the carrier's done more than just push new promotions -- it's benefited from them as well.

T-Mobile has added more than one million subscribers each quarter for the past 10 quarters, and already said that it will match or exceed the 2.1 million net adds for third quarter 2015, as it did in the previous quarter. Legere also spilled some of the beans at the Goldman Sachs Communacopia Conference, saying that T-Mobile exceeded last year's branded prepaid net customer additions in during the quarter and tripled the amount of branded prepaid net customer adds sequentially.

And with the 30% increase in iPhone pre-orders this year, it appears the company is starting its next quarter with lots of momentum. Of course, it's still unclear how many new subscribers are signing up for T-Mobile because of the new T-Mobile promotion. But with such a huge year-over-year increase in pre-orders, T-Mobile can at least be confident that it's helping to lock in current users on its network and is likely attracting some new ones with its very low pricing. 

Chris Neiger has no position in any stocks mentioned. The Motley Fool owns and recommends Apple. 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.