Apple has introduced the iPhone Duo, its first foldable iPhone and the largest-screen iPhone announced by the company. The $1,999 book-style device opens from a 5.4-inch outer display to a 7.6-inch screen for video, gaming, work and multitasking. AT&T CEO John Stankey said foldables have attracted a dedicated Android audience but remain niche, although Apple could broaden adoption among iOS users. He said demand would likely center on customers seeking a larger device and willing to pay more, and might consider buying the Duo if it could replace his iPad.