I guess MS is late by 19 years. PFU Limited reinvented the keyboard in 1996 :-P http://en.wikipedia.org/wiki/Happy_Hacking_Keyboard
That doesn't fold though. It's a foot wide and 4cm thick. The whole point of this new keyboard here is that it folds, and that it's really thin, so that it's like 6" x 5" x 1cm, and can go in your handbag or coat pocket. Much better prior art here: http://www.amazon.co.uk/Palm-Vx-Portable-Keyboard-105Keys/dp... (has 2 fold points, feels like a laptop keyboard)
They were absolutely wonderful. I could unfold the keyboard, turn on the Palm, and be taking notes in a meeting or on an airplane, in seconds. Plus, the Palm devices had killer battery life despite the battery technology of their time, and some usability concepts that were way ahead of their time.