On Friday, the Samsung Galaxy Z Flip foldable phone went on sale just days after it was formally announced at the Samsung Unpacked Event in San Francisco. It comes out a week after the Motorola Razr -- another foldable-screen clamshell phone -- hit stores. The Razr and Galaxy Z Flip have a lot in common, but they're also very different phones. Together they represent some of the biggest design changes to hit phones in years.
