Extra-large phones have been hot stuff in some countries for a long while, but not so much in the US. The country must have had a change of heart in the past few months, however. Kantar Worldpanel estimates that gigantic devices jumped from 6 percent of American smartphone sales in the first quarter of last year to 21 percent in early 2015. Why? If you ask Kantar, the launch of the iPhone 6 Plus was partly responsible -- it racked up 44 percent of all supersized phone sales despite being just a few months old. The analyst group isn't saying much in public how other brands were doing, although it's safe to say that category pioneer Samsung grabbed a large slice of the pie thanks to high-powered behemoths like the Galaxy Note 4.