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Polaroid. Walkman. Palm Pilot. iPhone?

The iPhone is arguably the most valuable product in the world, representing the backbone of Apple Inc.’s half-trillion-dollar hardware business and undergirding its software-peddling App store. If history is any indication, though, America’s favorite handheld device will someday take up residence with the digital camera, the calculator, the pager, Sony’s Walkman and the Palm Pilot in a museum. Although it’s hard to imagine the iPhone dying, change can sneak up rapidly on contraptions that are deeply entrenched in American culture.