how does someone change their phone number and does it cost money?

I can change my phone number 2 times a year at no cost. I haven’t used that option for ever. Still have my same phone number I had for years

You can buy a cool number from numberbarn.com and get it ported to your carrier.

I guess it probably depends on the carrier.

I called my phone company and did it a couple of years ago because someone was spoofing my number (weird getting calls from “myself”). The company changed it within minutes at no charge.