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

OJFord 5y ago
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?
- jcrites 5y ago
  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.)
  - OJFord 5y ago
    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.
- nickff 5y ago
  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_Numbering_Plan_area_codes 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”
  - account42 5y ago
    But even then, the + is not a separator but a placeholer for the international call prefix in your area.
- neohaven 5y ago
  > 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#Modern_plan https://en.wikipedia.org/wiki/North_American_Numbering_Plan#... https://en.wikipedia.org/wiki/North_American_Numbering_Plan_expansion 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.
- cesarb 5y ago
  > 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).
- archduck 5y ago
  Do they get routed differently then? (911 ringing up the dispatcher who's fielded the most heart attacks)

OJFord 5y ago

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?

jcrites 5y ago
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.)
- OJFord 5y ago
  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.
nickff 5y ago
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_Numbering_Plan_area_codes 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”
- account42 5y ago
  But even then, the + is not a separator but a placeholer for the international call prefix in your area.
neohaven 5y ago
> 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#Modern_plan https://en.wikipedia.org/wiki/North_American_Numbering_Plan#... https://en.wikipedia.org/wiki/North_American_Numbering_Plan_expansion 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.
cesarb 5y ago
> 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).
archduck 5y ago
Do they get routed differently then? (911 ringing up the dispatcher who's fielded the most heart attacks)