Cutting Random Shapes Into a Model?

So let’s say you’re modeling a low poly model and you’re just using basic shaders. How would you go about cutting shapes into a models surface that you could then assign shaders too? Instead of doing a UV map.

But just cutting into the face, so it stays flat, not adding other shapes and depth.

For example, cutting these basic faces into a phone, like the circle button on this image:


try the knife project tool: https://www.youtube.com/watch?v=jKJ-ml5N0fw