BARCELONA -- A pair of midrange smartphones wasn't the only hardware that Microsoft unveiled at its first Mobile World Congress since finalizing the purchase of Nokia's devices business.

The company also debuted the Universal Foldable Keyboard, a thin, portable keyboard that connects through Bluetooth to the iPhone and iPad, Android devices, and Windows Phones and tablets.

It's a small square of a device, with a matte grey finish and a magnetic closure that keeps the two halves together. You unfold it to see a keyboard that's split down the central folding seam. Some keys are larger than others, but they're responsive and spring back when you type.

I didn't get much time with the accessory for tablets and phones, but I was able to type about a paragraph's worth of text. To me, it's one of those physical configurations you have to get used to using. I noticed I made a lot of initial errors, though typing did feel fast.

Otherwise, the keyboard itself is fairly sparse, with just a Micro-USB charging port along the right edge.

Microsoft announced the Universal Foldable Keyboard along with two midrange phones, the Lumia 640 and Lumia 640 XL .

Catch all the news from Mobile World Congress!