999?
112 was in use in a few European countries, and then written into the GSM standard. That is why access to it is so widespread. It was even codified in mobile standards that the number should be reachable without a SIM in a phone.
999 is the very-long-established emergency services number in the UK. This was established pre-switched phone networks, at a time when rotary dial phones were all you had and pulse dialling was the standard - on both sides of the Atlantic. 111 was not used (the fastest number to dial on a rotary phone) because telegraph lines, clattering together in the wind, could accidentally dial 111.
111 was not used because if you were in the grip of an emergency you may be too panicked to dial 111 accurately on a rotary dial. 999 was the most easily entered as all you had to do was dial to the end of the rotary.
If your telegraph line theory stand any ground then surely they'd've used 222 or 333?
I have to ask if you've seen, let alone used a rotary dial phone?
You stick your finger in the appropriately numbered hole, and turn to the stop. 111 or 999, both would be dialled as accurately as the other. The issue is pulse dialling, now long-superceded by tone dial.
Find a real telecoms engineer and they'll confirm the correctness of what I've said. I have several in my family, grew up at a time when rotary phones were still commonplace, and prefer to know things than spout poorly formed guesses.
I have to ask if you've seen, let alone used a rotary dial phone?
Do you? Do you really? ¬_¬
In lieu of finding a real telecoms engineer (as opposed to one of those troublesome fake ones), or encouraging members of my family to enter the trade and by some indeterminate means transfer their specialised knowledge into my own, I'll simply leave you in your ivory tower to guard the pillars of pedantry.
You're both wrong according to Wikipedia (although that bit about lines connecting and accidentally calling 111 is true... but then 999 is a very commonly butt-dialed number, leading to an enormous number of fake calls (112 and 911 don't have that problem)).
Apparently it was all down to practical money saving reasons. It was easier to modify the pay phones of the time to dial 999 for free than any other series of numbers (because 0 was already free). Bah, humbug. What a ridiculous reason. I much prefer the reasons presented by the people here on this page. Anyway, here's Wikipedia's more detailed explanation: http://en.wikipedia.org/wiki/999_%28emergency_telephone_number%29#History
Actually, If you've ever used a genuine rotary phone, 999 is much easier to accurately dial in a panic than 111. Most rotary phones would only have a stop at the end of the wheel (9) making it nearly impossible to botch. Dialing "1" three times in quick succession however it could be very east to overshoot-especially if the caller's hands were shaky - accidently dialing 2, 3 etc... Just find an old rotary phone and try it some time, You'll immediately see what I mean.
Bzzzt! Wrong!
And, I'm old enough to have grown up with rotary dial. The stop is at the low-digit end. You stick your finger in, and turn the dial to the stop. The arc traversed to dial a 9 is the longest.
But, thanks for playing.