[spectre]

There's some interesting technical history behind some of the emergency number choices:

999 in the UK (from 1937) was chosen because public payphone could be easily modified to make it a free call.

111 in New Zealand (from 1958) was chosen because the system was implemented using British Post Office equipment that already supported 999. But New Zealand phones pulsed in reverse so 111 on a New Zealand phone produced the same pulse as 999 on a British phone.

000 in Australia (from 1961) was chosen because 0 was already used for trunk access. On an automated rural exchange, 0 would connect you to a main centre. In remote communities it was 00. This meant that dialing 000 through an existing remote exchange would at least connect you to an operator in a main centre.