Will there be a cellphone outage as well in the various regions that lose electric power?

It is very likely that cell phone coverage will be spotty or absent in many regions affected by the loss of electricity. There will be a limited capacity for backup systems for a relatively long-term outage like this of multiple days. Usually, such outages are for relatively short periods of time, a few hours at most, and there are backup systems in most cases for routing power to keep some essential services going. These days, cell phones are the only lifeline many have.