You can compare verification codes on WhatsApp and (starting ~next week) iMessage [1]. And both are in the process of establishing a mechanism similar to Certificate Transparency for x509 certificates [1][2].

[1] https://security.apple.com/blog/imessage-contact-key-verific...

[2] https://engineering.fb.com/2023/04/13/security/whatsapp-key-...