The only people who would give one of these numbers out in real life are people who otherwise don't want to give you a real number.

Anyone who needs a number for a legitimate reason should do their own validation anyway.

You can try calling them but they return "number disconnected" messages.

I have one of these that I use when dealing with retailers for which the phrase "I don't have a smartphone" does not compute. Saves the hassle of having to explain it every time, and so far I'm the only one using my made up number, so they "remember me" or whatever. But they can't actually call, and that's the point.