Earlier quoted context omitted.
Or better try telephone region codes, which are ambiguous when a phone number is written as a consecutive string of digits, without +/()/-/space.
You say this as if it’s a universal thing, like IATA codes, but I assume it’s a quirk of some particular country? My region code definitely does not have this. Sounds pretty nuts to me btw, how does that work when you turn it into standard E.164 format like “+123456789”?
Many countries (if not all of them) use localized numbering format - short numbers to hit the local destinations (intra-city calls), numbers with city prefixes to get to the numbers in a different city within the same country, specific prefixes (i.e. 00) for international calls, etc. The most convenient way of processing this mess is to rewrite the numbers (called/calling) on the ingress, into e164, and then processing the call using the routing table/rules of the pbx. On the egress the numbers may be rewritten again using the local numbering rules. This is how I built the international telephony system in one of my previous companies at least.
Some countries are easier in their numbering system (Singapore being an obvious example) and some are not (China doesn’t disclose number ranges allocated for different regions/cities, which makes the renumbering step more difficult)