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Comment by OJFord | Hacker News Reader

What if you want to dial an external line that begins 11? How long should it wait before deciding you're stopping at 911?

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The short answer is it doesn't, it just dials 911.

Way, way back in the day when dial-up was a thing, I worked at a company that had an automated system that called a large bank of test numbers to make sure they were still working. This system ran 24/7. It required you to put in the numbers as <areacode>-<number> without a prefixed 1. The code would add the 1 automatically. Because it operated in a lab inside of our phone system, it dialed 9 to dial out. Well, at some point someone had to reconfigure this system and I guess thought it would be good to add a 1 before each # in the configuration.

This resulted in thousands of 911 calls being made to our local call center. We had accidentally created a 911 war-dialer.

The moral of this story is don't dial 9 to get an external line. You're literally a keystroke away from calling 911 every single day.

In Australia the Emergency number is 000.

I ran into a similar issue with software that was trying to dial 0 for an outside line, and then a number starting with 00.

Lots of very unhappy people.

As with any short answer the real answer is “it depends”. Any modern internal phone system has a dial plan and the default will certainly call 911 but you can certainly change it. I used to work inside a call center where you had to dial 91 to get an outside line. You can imagine how many people accident dialed 911. Since we couldn’t muck with 911 we made outbound dialing straight from the sip client only and not through the handset and told people not to dial outbound to order lunch or whatever from the handset. We didn’t care about them ordering lunch just couldn’t muck with 911. But that being said I could have most certainly changed the dial plan instead and screwed with 911.

This is a classic in America when calling Europe or International.

The dial out in corporate, usually you used 9. Then you google how to dial in Europe because the numbers are not natural. Google mentions dial 11 + country code + phone number.

So people hit 9 to dial out, then 11 to dial in Europe. Instantly you hear: Emergency 911, is this an emergency?

The dialer is like: no I'm trying to call Europe.

Wikipedia claims you should dial 011, so does that mean those people should have correctly dialled 9011?

9+11 specifically. Yes, a plus sign. 0 is also supposed to be mapped to plus or passed on when dialing external for compatibility reasons.

International number dialing is confusing as hell. I've got a BSEE and law degree and I can't figure it out 80% of the time.

No, 9011 is correct. "011", the international exit code for calling from the US, is what the + gets mapped to in a number such as "+49 xxx". It is followed by the destination country code (which starts with a 3 or 4 for Europe [1]), and then the local number. So for example, to call a number in Germany from a PBX in the US:

9-011-49-(German number) [3]

For long-distance domestic, the national trunk prefix should be used instead. For the US, this is 1 (unrelated to the US country code, which is also 1):

9-1-(10-digit US number)

For local calls, you do not need the trunk prefix, so you would dial:

9-(7-digit US number)

However, no US (or North American) area code nor central office code starts with a 1 [4]. So even in the above two cases, the sequence "911" should never occur.

[1] https://en.wikipedia.org/wiki/List_of_international_call_pre...

[2] https://en.wikipedia.org/wiki/List_of_country_calling_codes#...

[3] https://dcloud-cms.cisco.com/help/outbound_dial_patterns

[4] https://en.wikipedia.org/wiki/North_American_Numbering_Plan#...

Never? That just means you cannot use 9 for calling an external line at all.

Using 9 for dialing out is a terrible setup that nothing should use.

Never what? Sorry I don't follow.

The rule is really simple: If you dial 911, you must be immediately connected to the emergency services. This means that there cannot be any other number that starts with the prefix 911. If this means that you have to shuffle around what number you use to call an external line, then you just have to do that.

They upgraded our PBX so that you can just dial the number as it is and the software figures out internal or external or 911. The 1 key on a lot of our phones was bouncing so 9-1-800-bla-blah would turn into 911 way too often. So they changed to not require the 9.

Can we not just change the 9 for an outside line to a 0 or 3 or something?

Seems like we put too much stuff on the 9, it's not like we're still using rotary phones

Bizarrely, my work office phone (at a US Federal agency no less) was switched from 7 for an outside line to 9 just before the pandemic hit. People really like 9 for some reason.

Normally 0 or + are supposed to be used for external lines. Then you would call 00 for an international call.

In the North American Numbering Plan, a phone number (neither 7 digit or 10 digit with the area code) can start with a 1.

And no 'special' ones (like 911)? e.g. 112. Relatedly, countries usually implement each other's codes for tourists' and children who watch foreign films' benefit - 999, 911, and 112 will all work in the UK for example.

And when you say area codes [can't] start with a 1, is that only when you include a 0 prefix?

Country codes can start with 1. There doesn't seem to be a +11~, but is it forbidden? Are there no US or Canada (+1) numbers that start with even a single 1?

Depends on what you mean, but there are no 1XX area codes in North America, so there is no reason you’d ever dial 9 (for outside line) 1 (country code) 1 (first digit of area code).

https://en.m.wikipedia.org/wiki/List_of_North_American_Numbe...

Of course you could make “91” be the code for outside lines, forcing someone to dial “91+1-XXX-XXX-XXXX”

But even then, the + is not a separator but a placeholer for the international call prefix in your area.

> Country codes can start with 1. There doesn't seem to be a +11~, but is it forbidden?

No country code (or phone number) can be a prefix of another. There cannot be a +11 country code, since after the first 1 you are already within the NANP "country" (and it seems the NANP rules disallow area codes starting with 0 or 1, so the next digit can only be on the 2-9 range).

The North America Numbering Plan does not allow any (normal) phone numbers that begin with the area codes 000-199. So there can be no valid numbers that are of the form +1 (1nn) nnn-nnnn.

(There are special dialing codes like dialing 011 for international that are an exception to this, but no normal phone numbers.)

That's what I meant by 'special', say you had a 118 for some other purpose, you couldn't dial it (unless also special cased as not needing a 9 dial-out prefix) as 9118.

> There doesn't seem to be a +11~, but is it forbidden?

Well, kinda... The thing is, even if not required by standard (It is, there's a Numbering Plan for the US and Can), most 9-to-dial-out systems would fail to call such a number, redirecting 911-anything to immediately dial out 911 once the second 1 is dialed.

IIRC, I've seen POTS also skip the inter-digit tone wait (the time between your last dial and the system going "okay, that's all the numbers, let's call!") when calling x11 numbers, generally considering "911" and other emergency/service numbers to be a magic triple that doesn't wait for other numbers to dial out.

There are no area codes starting with 1 in the US nor Canada to my knowledge since any dialing in a system with 9-to-call-out should end up being dialed as follows :

* 9 (leave system)

* 1 (country code)

* 1 (first digit of the area code)

And there is no step 4, because 911 is a special number like 411 and 311, that has a special dial plan. Since there is a possibility of issues if we make the treatment any less dumb, we don't do that. 999 is a special, unassigned code in the US too. 112 is likewise impossible to clash with here in NA since calling that with a corp system just means typing 9112, which ends up being 911, and dialing it on its own can also be allowed to be a special case since there are no area codes with 1 because of 911.

In fact, even "small area codes" or, officially, "office codes" are also required to not be X11. You used to be able to call locally in your area code without dialing the area code, too. It ends up being that xxx-911-xxxx is also an invalid number. Because locally, you would have had to type "911" to start dialing that number. There are also other limitations that can be seen here as well as allocation for future expansion : https://en.wikipedia.org/wiki/North_American_Numbering_Plan#... https://en.wikipedia.org/wiki/North_American_Numbering_Plan_...

There's also probably a physical, legacy reason it's probably much more difficult to make a physical 911 switch when "911" is also a valid part of a phone number. It means you need to figure out "Is it what they meant, or are there more numbers coming?" It means the sequence of operations "<open line><9><1><1>" always means emergency, fast connect, and probably easier to implement as a side-channel than as a part of the dial logic? This is speculation, I haven't actually opened a POTS PBX with a physical implementation of the 911 dialing logic.

Do they get routed differently then? (911 ringing up the dispatcher who's fielded the most heart attacks)

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