>>>I am not sure whether your system is different from our system, I doubt it. In Norway toll free numbers are linked to a number of "normal" numbers by the telephone companies. The link automatically goes to the nearest physical unit, so that people with local knowledge will answer.
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>>Well, in USA certain area codes such 800, 888, 877, 866, 855, 844 and 833 are toll free numbers. This is said in the link I quoted. I just want to find out if this is how it always has been and if this is how it's going to remain.
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>>In other words, my question is more about these numbers themselves and not how they are really working. Say, if I have a list of phone numbers, I want to filter the numbers which are toll free numbers and I need to make sure I will apply correct filtering based on the above numbers.
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>>I also have a question about premium paid numbers. I read this article in Wikipedia
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>>https://en.wikipedia.org/wiki/Premium-rate_telephone_number
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>>which seems to indicate that in addition to 900 area code the 976 code was used at some point. I want to find out if any other numbers can be considered paid premium services.
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>Seems like I misunderstood your question. Anyway, I have worked with phone systems for most of my life, and I have always tried my best to stay updated. I have also read many articles about the solution you have in your country.
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>I noticed your sentence "I just want to find out if this is how it always has been and if this is how it's going to remain." First of all, it has not always been like it is now. :-)
>And nobody can say anything for sure about the future, but I can tell for sure that I haven't read anything that indicates any change in the foreseeable future.
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>What I would do in your specific case, is to store the area codes in question in a lookup table, so that you don't have to change anything (or at leas very much) if anything changes.
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>I can tell you that here in Norway we stopped using area codes roughly twenty years ago. It came as a little shock to everyone, but now nobody thinks anything about it. And all toll free numbers are five digits, starting with a zero, like 05002. Since we don't use area codes, they can easily change that into being 6 digit numbers, or 7. Also, we don't use wired phones anymore, meaning that no number is actually dialed until we press the green Call button.
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>The last few months has taught me that many things that never ever should happen, can in deed happen anyway.
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I like the idea of placing these area codes into its own Lookup table, I'll go ahead and do that now (in our case right now the SQL Server DBs are in Azure and there are no cross-referencing queries yet in the model we're using but we're considering a possibility to switch).

I just want to make sure I have all such numbers correctly identified as of present and I also need to be notified when they change (if they do). It is also not clear if 822 is already in service or not (most of the links I checked don't have that number, except for that confusing PDF I found). I did email NANPA so hopefully I'll get the answers to my questions.