WIFI Calling as Phone Backup
Liquid Fluoride said internet or text is best way to communicate during disasters, and articles on how people were able to communicate during Harvey backs up what LF recommends.
WIFI calling was highly recommended. Some phones have it as an optional feature (mine does so I turned it on yesterday. It's free on my plan). For those who don't have it preinstalled you can download an app.
With WIFI calling you can call anybody - they don't need to have an app (at least that's my understanding. Haven't had a chance to test it yet).
Will report back if I have to use it.
We depend on WiFi calling at our house here on the north shore of STX as our Sprint service is pitiful - it works great. You can make and receive calls from anywhere that has Wifi. I believe with Sprint you can activate it yourself but with AT&T you used to have to have them activate it for you. There is no monthly charge for it.