999 was crappy design for "emergency" as, in the analog era, it would take almost 9x the time to dial it as that of a number like 111 or 112.
The whole point of 999 was that a nine was the only number you could guarantee to accurately dial blind on a rotary input device with only your sense of touch and a little knowledge about the device itself available to you.
I'm also not too sure why any other number would be preferable. 999 really stands out whereas all the other emergency numbers across the world do not. I'll accept that because I'm a Brit that I have been conditioned to 999 being THE emergency number might bias me somewhat but I think my point still stands: 999 is far more obvious than any other emergency number.
I do a lot of (modern ie VoIP) telephony work and can only think that the 9 for an outside line plus rubbish dial plans and crap hardware and programming meant that 999 might not work for some systems. I've also explored the "not British" criteria for the number ... 8)
Can anyone explain why 999 is not the best emergency number ever chosen?