Almost every phone manufacturer is trying to develop a handset with a truly edge-to-edge display. Most end up with a small notch, but others are finding new and unusual ways to hide the front-facing camera. Oppo, for instance, has packed a tiny motorized mechanism into its Find X flagship. At a glance, it looks like a regular phone with a 6.4-inch, 1080p display -- but as soon as you launch the camera app, the top section slides up to reveal a 25-megapixel selfie shooter and a dual-camera system on the back. Close the application and the cameras will automatically disappear again.