Something I learned from staying through a few hurricanes:

In an emergency, cell phone carriers might limit cell phone service to emergency calls only. If you can't call out during an emergency... try sending a simple word text instead. Don't add any emojis, no graphics of any sort, strictly text. Often those will go through. Just something to keep in mind.

Also keep those old cell phones (the ones in your junk drawer) charged for an emergency. Any cell phone, even inactive ones, can be used at any time to dial 911. All cell phone carriers are required to process 911 calls from any phone. If SHTF, it's always best to have a backup.

Lastly, don't be afraid to be creative. When Kingwood, Texas flooded during a tropical storm a few years ago, stranded residents had a hard time calling for emergency help. 911 and other help lines were all flooded with calls, so they kept getting busy signals. Residents were smart. One called a local Pizza Delivery restaurant (which answered the phone and sent help). Others called local businesses or radio stations for help. They got the word out and people with boats and trucks showed up. :>) Don't be afraid to try the unusual.