The iPhone models currently sold on apple.com work with nano-SIM cards from compatible carriers. And they work on many 4G LTE networks around the world. Contact service providers for details.
Information on iPhone X support for 4G LTE networks by carrier and country
Yes, you do. When you buy the iPhone from apple.com, it is sold unlocked. You can contact a carrier directly to learn about the tariffs available for iPhone.
*The iPhone X display has rounded corners that follow a beautiful curved design, and these corners are within a standard rectangle. When measured as a standard rectangular shape, the screen is 5.85 inches diagonally (actual viewable area is less).