Could you image what things would look like with rogue "DNS" servers that mapped bankofamerica.phone to a phisher controlled endpoint? You could no longer trust that calling the "number" on the back of your credit card would actually get you in touch with the actual bank.
The same problems would happen if someone mapped "google.com" to a phisher controlled endpoint. TLS solves that, and by extension, so does SIPS. Then add in SRTP, etc.
