I have managed to learn most of those the hard way. That said, the case in number 20 kinda surprised me though: My country did the same in the 90's and although

I have managed to learn most of those the hard way. That said, the case in number 20 kinda surprised me though: My country did the same in the 90's and although I was a child back then, I have a good recollection of how that happened: the transition was from analog to digital but the switch was almost seamless: overnight your phone number got a "9" prefix and that was it. That is unless your landline was yet to be installed, in which case you got an "8". Whenever you dialed the old phone number without the prefix, you simply got a busy line. The old number was no longer valid and you could not reach it. The aftermath was people forgetting to add the prefix and thinking the other person was constantly on the phone(or using the internet cause... dial up). Now inter-city calls were also associated with adding a city code to the number, so in my case for instance, if you wanted to call me from another city, you had to prepend 02. But those were also easy: all city codes were 2 digits. People from the capital had 6 digit numbers before switching to digital and 7 after. All other cities were 5 before and 6 after respectively. I think the people from (at the time sole) telecom did their homework for once in their history and realized that they had to make it stupid simple for elderly people living in the countryside and having all their numbers written down in an old notebook that's falling apart as it is. That said, there were exceptions to the capital vs non-capital phones. Namely dial up internet providers. They always had 5 digit numbers and on some rare occasions 8. Mine had 8 and funnily enough, I still remember the number...