According to a report from market research firm Kantar Worldpanel, smartphone sales in the U.S. have remained stable over the three-month period ending in May. The firm noted that strong iPhone sales from T-Mobile helped Apple’s market share jump 3.5% between March and May, and the iPhone now accounts for 41.9% of smartphone sales in America. The mobile market duopoly continued as Android accounted for 52% of sales, up 0.1% year-over-year. Sales of Windows Phone devices saw little growth, increasingly a mere 0.9% year-over-year for a 4.6% market share in the No.3 spot.

Even though it was released in mid-April, the iPhone accounted for 31% of smartphone sales at T-Mobile in the three-month period ending in May. Kantar noted that the iPhone helped T-Mobile attract first time smartphone buyers, adding that more than half of subscribers who purchased an iPhone from the carrier upgraded from a feature phone.

Despite the success of the iPhone, T-Mobile’s smartphone market share fell 3.4% to 10.1%, behind AT&T at 34.6%, Verizon with 29% and Sprint at 12.7%.