Our recent experience with hurricane Irma confirms the wisdom of not putting all of your communication eggs in one basket. The storm interrupted communications for hours and days. Immediately afterward, my phone had a good wireless RF connection to T-Mobile’s cell site, but no IP (Internet Protocol) connection. Text messaging using SMS (Short Message Service) worked fine. (SMS is a telephone — not Internet — protocol. It uses the telephone industry’s venerable Signaling System 7 to transport its messages.)
On the other hand, messaging apps such as WhatsApp, Facebook Messenger, and SnapChat rely upon IP to transport their messages. Without an IP connection, these messaging apps wouldn’t have worked. The plain Jane texting program that’s built into my Android 5 phone doesn’t need IP. SMS originally used GSM for message transport. Now it also uses LTE, CDMA, etc.
T-Mobile provided SMS and voice calling service for days after the storm, before they restored my IP connectivity. They said that about 700 cell sites in Dade and Broward counties had been degraded by hurricane Irma.
Caveat: SMS isn’t secure, as its transport mechanism, Signaling System 7, lacks an authentication protocol.