Never watch sausage being made.
The basic principles (aka best practices) are well understood.
However, money is the driving factor in all decisions whether
those decisions are made by the public or private sector.
9-1-1 (the US version of emergency number) service is very
reliable, but has been disrupted the same things which disrupts
telephone service in general. Not all public service answering
points have redundant circuits. Not all end-offices have diverse
paths. Even when redundant circuits exist, they've been groomed
on to a common physical facility. Operator and software errors
corrupt translation tables in switches. Much of the reliability
comes not from preventing things from breaking, but by priority
repair service when it breaks. Because 9-1-1 is usually repaired
before most other services, it has the best MTBF/MTTR even if it
breaks due to the same cause as other services.
Of course, there is always the definition of working. If your phone
doesn't work, you can't call 9-1-1, even if the PSAP is "working."
Another problem in New York City was NYC's emergency operation center
"bunker" was destroyed in the collapse of the world trade center
tower. In addition to all the other problems, Verizon needed to
install/re-route emergency circuits for almost everything connected
to the EOC.