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The smartphone OS race has not seen a significant shift in the last year, but Apple's iOS has managed to pick up a little steam in the U.S., according to new stats from Kantar WorldPanel ComTech.

In the three months ending May 2013, smartphone sales were 'relatively stable,' Kantar said, but iOS grew 3.5 percent as compared to the same time period in 2012. Given that Android didn't really see a change, Apple managed to edge in on its top rival's lead.

Specifically, about 52 percent of smartphones sales by the end of May were for Android devices, while iOS landed at 41.9 percent, and Windows Phone was at No. 3 with 4.6 percent, up 0.9 percent in the last year, Kantar found.

Kantar suggested that the launch of the iPhone on T-Mobile helped boost the Apple operating system.

'The highly anticipated release of the iPhone on T-Mobile has benefited iOS in the latest 3 month period, though it has not yet impacted T-Mobile's share in the market,' Dominic Sunnebo, Kantar's global consumer insight director, said in a statement.

Most T-Mobile iOS buyers opted for the iPhone 5 , Kantar said. Overall, 31 percent of smartphone sales on T-Mobile during the three-month period were for the iPhone. That's lower than AT&T (60.5 percent) and Verizon (43.8 percent), but 'a full quarter's worth of purchasing next month may impact T-Mobile's overall sales share,' Kantar speculated.

A number of T-Mobile iPhone buyers - or 53 percent - were upgrading from feature phones, Kantar said. Among those planning to buy a new smartphone in the next year, meanwhile, 28 percent are eyeing an iPhone, so there are other opportunities for growth at T-Mobile.

Overall, 34.6 percent of smartphones purchased in the three-month period were for Verizon, 29 percent were for AT&T, 12.7 percent for Sprint, and 10.1 percent for T-Mobile.

Apple's next version of its operating system, iOS 7, is expected in the fall alongside a new iPhone. For more, see PCMag's review of the T-Mobile iPhone 5 and the slideshow above.