T-Mobile's uncarrier strategy appears to be getting a little help from sales of Apple devices. According to recent numbers from Kantar Worldpanel, T-Mobile grew to 13.2 percent of smartphone sales in the U.S. market in the 3 month period ending August 2013, marking its highest share of sales over the past year. 

The share represents growth of 1.1 percent, reversing an on-going trend of year-on-year decline. The iPhone 5 remained the top-selling smartphone at T-Mobile, with 17.1 percent of sales.

Kantar's global strategic insight director, Dominic Sunnebo said that when iOS first debuted on T-Mobile in mid-April, the majority of sales came from consumers upgrading from a featurephone to their first smartphone. 

"However, looking at those who purchased an iPhone in the August period, 56 percent of those consumers came from another smartphone, including 38.5 percent from an Android device,” Sunnebo said in a statement.  

The Kantar numbers shows Android retaining its lead for the period, with a 55.1 percent share of the market. Apple's iOS follows with 39.3 percent share, an increase of 5.4 percent versus the same period a year ago.

Little movement is seen among the other operating systems in the market. Windows saw 3.0 precent of sales in the August period, while BlackBerry was down to just 1.8 percent of sales.

Verizon sold the most smarpthones, with a 37.1 percent share of all sales, which amounted to growth of 6.9 percent. AT&T maintained second at 21.7 percent, and Sprint took home third with 14.6 percent of smartphone sales.