How to find out if a phone number exists and works anywhere in the world?

Question

Telephony

How to check if a given phone number exists? Anywhere in the world. That is, the number format may be correct. But, what if it doesn't work or something else? How do the services that do it? Interested in the algorithm.

Answer 1

Everything is very simple. We take a number from any telecom operator that is connected to a public network and has routing in accordance with the communications law of its country. This will be our verified number. Next, we take a number from each telecom operator on the planet and try to call the number being checked. We write down failures and victories, then "voila" we get a map of the connections to your number (and not only)) from anywhere in the world.
ZY: there is of course another, even more literal interpretation of the question, in terms of radio communications, for this you will really have to try to call from anywhere in the world.