Pair a Keyboard to iPhone?...why not use Surface Pro Type Cover keyboard?

Help! I use a Surface Pro (Windows 10) and an iPhone. Since iMessages are not supported on Windows 10, I need a way to attach a keyboard to my iPhone (next best thing). I was about buy a Bluetooth keyboard and thought... "wait a minute, my Surface Pro Type Cover (keyboard) is a Bluetooth device. Why can't I pair it with my iPhone? Has anyone done this? If not, is there another way to get iMessage to work on Windows 10?