Who is running the interface between the web and the phone network? That’s what I don’t understand here. Such services, e.g. Google Voice, still require registration — they aren’t as free as the web itself.
Brother’s service is free. Pretty sure HP’s is as well. He will have to use his phone to receive through an app, but should be able to send if he has one of the later models and it’s got access to the web through his router.