Apple’s iOS has notched up its market share in US smartphone sales by 3.5 percent through the three-month period ending May 2013, according to a report by research firm Kantar Worldpanel.

Kantar says smartphone sales overall remained relatively stable in the US over the three months compared with the same period last year. Android remained unchanged (tacking on a meager 0.1 percent), while iOS climbed 3.5 percent in the period, narrowing the gap between the two operating systems.

The research firm attributed this to the release of the iPhone on T-Mobile. In late March, T-Mobile said it would begin offering the iPhone 5 starting April 12, available on its new 4G network for $99.99 down, plus $20 per month for 24 months.

Despite only being released in mid-April, Kantar says that the iPhone 5 became the best-selling smartphone at T-Mobile for the three months ending May 2013 — accounting for 31 percent of the carrier’s smartphone sales.

Kantar Worldpanel ComTech global consumer insight director Dominic Sunnebo said:

iOS’ strength on T-Mobile appears to be the ability to attract first time smartphone buyers, upgrading from a featurephone. Of T-Mobile consumers who bought an iOS device since it launched on the carrier, 53% had previously owned a featurephone, well above the market average of 45% of iOS owners who previously owned a featurephone.

Even though the share of iPhone sales at T-Mobile is still lower than AT&T (where iOS accounts for 60.5 percent of sales) and Verizon (43.8 percent), Kantar notes that a full quarter’s worth of sales next month may push T-Mobile’s overall sales share up. The research firm also found that 28 percent of T-Mobile customers planning to change their mobile devices within the coming year want to switch to an iPhone.

However, according to Kantar, Android is still the number one operating system in the US, leading smartphone sales at 52 percent. iOS follows behind with 41.9 percent of sales, while Windows remains in third with 4.6 percent of sales, up 0.9 percent compared with the same period last year.

Comparatively, another market research firm, comScore, says that for the three-month period ending April 2013, Android’s market share dropped for the fourth month in a row to reach 52 percent, while Apple increased its share by 1.4 percentage points to make up 39.2 percent.

Even though the figures may differ slightly, both sets show that the Android-iOS duopoly in the US has reached a new high (91.2 percent market share as measured by comScore and 93.9 percent based on Kantar’s data).

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