This hits me too because I travel a lot. Try installing Signal on your phone when your only connection to the world is over WiFi. Try getting an SMS when you're not on a compatible network. You can't. That doesn't mean I don't have my phone with me. The requirement for a contactable phone number instead of an email address or other message is like pretending that your IP address and your hardware MAC address are the same thing, when they're obviously not. One identifies an actual piece of equipment, and the other is literally just bits on the wind.