That didn't take long. Just months after finally getting the iPhone in its lineup, Apple's (NASDAQ:AAPL) device is already surging at T-Mobile (NASDAQ:TMUS).

According to the latest data out of market researcher Kantar Worldpanel ComTech, the iPhone 5 quickly became the top smartphone on the No. 4 domestic carrier, even though it was only launched halfway through the period in question. For the three months ending May, the iPhone grabbed 31% of all smartphone sales on T-Mobile.

Those early gains are helping Apple more than T-Mobile, though, as T-Mobile's share of total domestic smartphone sales declined slightly to 10.1%. Kantar director Dominic Sunnebo noted, "The highly anticipated release of the iPhone on T-Mobile has benefited iOS in the latest 3 month period, though it has not yet affected T-Mobile's share in the market."

Operating System

3 Months Ending May 2012

3 Months Ending May 2013

iOS

38.4%

41.9%

Android

51.9%

52%

BlackBerry

4.6%

0.7%

Windows

3.7%

4.6%

U.S. market share. Source: Kantar Worldpanel ComTech.

iOS is catching up with Google Android in the U.S. market, comprising 41.9% of domestic sales. The digits also corroborate Microsoft's successful win over BlackBerry, with the software giant grabbing the No. 3 spot.

A large chunk of those iPhone buyers on T-Mobile (53%) were first-time smartphone buyers, which is an increasingly important segment of the market, as the high-end is becoming saturated. You only get one shot at a first impression, and grabbing first-time smartphone buyers in a sticky platform is a key opportunity that's not lost on Apple.

T-Mobile's composition of iPhones is still smaller than the two largest carriers, Verizon Wireless and AT&T, but in line with Sprint. However, remember that the device was only on sale for half of the period, and Kantar believes the composition will change with the next full quarter of iPhone availability and T-Mobile may also be able to grow its share of smartphones.

The good news for T-Mobile is that it's not facing massive subsidy expenses thanks to its new "un-carrier" approach. While larger carriers are on the hook for hefty subsidies commensurate with iPhone sales, T-Mobile's new financing plans mean customers are footing the bill instead. After initially touting the new sales model as "dramatically different," T-Mobile quietly withdrew its promotional discounts and now sells iPhones at full retail price. The financing plan will still likely earn it two years of loyalty, though, since most people aren't willing to pay full retail price.

Apple could see even more upside within T-Mobile's customer base once it releases its mid-range iPhone this year, particularly since that device should fare well in the prepaid segment that is T-Mobile's forte.

Fool contributor Evan Niu, CFA, owns shares of Apple and Verizon Communications. The Motley Fool recommends Apple and Google. The Motley Fool owns shares of Apple, Google, and Microsoft. 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.