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Phablets — smartphones that fall somewhere between phone-sized and tablet-sized — claimed 21 percent of all U.S. smartphone sales in the first quarter of 2015, nearly quadrupling their 6 percent share of total smartphones from the first quarter of 2014, according to new research from Kantar Worldpanel ComTech.

Apple’s iPhone 6 Plus (VB review) accounted for 44 percent of phablet sales in the quarter. Customers cited screen size as the main reason for buying a larger phone, Kantar said. (Duh.)

Overall, iPhones accounted for 59 percent of AT&T’s smartphone sales in the quarter, 43 percent of Verizon’s, and 50 percent of Sprint’s. Samsung smartphones dominated T-Mobile sales in the quarter, with 42 percent.

Apple’s iPhone 6 and 6 Plus already represent 18 percent of all iPhones in use in the U.S., and 64 percent of iPhones in the wild are iPhone 5s or newer models. This bodes well for Apple Watch sales, because the new wearable interacts only with those newer iPhones.

However, people who switched from Android to iOS were down during the first quarter. Only 11.4 percent of iPhone buyers switched from Android, compared with 14.6 percent in the year ago quarter.

Among new Android customers, only 5.9 percent came from iOS, compared to 9.8 percent in Q1 2014.

LG had a particularly good first quarter, Kantar said, growing its market share to 10.8 percent from 7.4 percent one year ago, while Samsung held onto second place as it prepared for the launch of its new Galaxy S6 and S6 Edge in April.

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