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The article is absolute trash for not mentioning this. “Their iconic keyboards…” is the closest it gets to describing them.
Thankfully, there is a link to the patent at the end.
Abstract
A keyboard comprising a plurality of transparent keys. In use, the keyboard is attached to a device such as a mobile device, to overlie a display screen of the device. One or more images displayed on the display screen are made visible to a user through the keys, which may be pressed by a user. User input is determined by identifying a pressed key, and the image or part thereof visible through the key when pressed.
Basically a detachable keyboard of transparent material as a display overlay, providing tactile feedback while the LCD allows for backlit and customizable key labels. I don’t remember seeing a practical implementation of this IRL or in media but I might be too young for that.
Even after they stopped producing phones, they could have made a killing licensing the patent to phone case manufacturers.