Where are the phone numbers being generated in jitsi-meet

Hello there,
I’ve installed "react-jitsi" npm package in my react application and I want to know "where are the phone numbers being generated from and who is paying for the cost of those numbers?"
Would you please provide me above detail it is very helpful to me and also please tell if “phone numbers being generated” then how can I do with "react-jitsi" npm package
Looking forward to your replay
Thanks