The natural instinctive inclination for just about everyone if wireline telephone service isn't available is to pull out the cell phone and make a call. In an emergency situation that knocks telephone service out of commission the people flooding the cellular networks making calls to check on relatives and friends would potentially overload cell towers, even entire cellular networks could get crippled.
The first thing it to limit the number and length of cellular calls. Use cell phone calls to check in with family members affected by emergency conditions and/or communications network outages. Secondly use text messaging as much as possible. Text messages may get delayed a few minutes depending on congestion on the cellular networks.
Anybody in the role of caregiver to family members who are elderly, disabled or have long term health conditions may need to consider a communications solution that works independently from the traditional telephone and cellular networks. FRS and GMRS two way radios that use UHF frequencies that have 20 km or more of range can be purchased for well under 100 dollars.
One of the essential needs for survival in an emergency is access to communications, having a plan to communicate with relatives and friends when telecommunications networks fail in an emergency situation could save your life that of someone you are about.