As for reliability, it's a toss-up between hard-wired local telephone
service and a cellphone.

Cost definitely favors VoIP via some flavor of high-speed internet.

In the event of a major power outage cell phones backup power is much
more limited than hard wired phones. also in max use like a disaster,
cell hones will lock out everyone except emergency workers. its
programmed in your phone at activation.

sometimes DSL works even when POTS is out, plain old telephone service
is POTS.......

in such a case VOIP may be better