] The emergency system broke down about 7:20 p.m. after a
] Verizon engineer who was making service changes to a
] bank's telephone numbers in Brooklyn inadvertently
] included numbers that are used to carry 911 calls, city
] and telephone company officials said. The numbers were
] close in sequence, the officials said.
]
] The 911 calls then ended up being rerouted to the bank's
] phone system, and callers heard a busy signal. City and
] Verizon officials said that while the backup system in
] place for 911 was functioning properly, it failed to pick
] up the calls because it was designed to catch a technical
] error, not a human error that would be interpreted as
] simply a change of instruction.

In a properly architected network the weakest point is the equipment configuration.

Verizon Plans Steps to Prevent Another Shutdown of 911 Line