They should be formatted in a way that can be understood by everyone, whoever they are, whatever system they are used to.
Importantly, we are not in Britain and we don’t have the pattern of area code+6 numbers. Neither are we in the USA and we don’t have the pattern of area code+7 numbers.
Historically, we had something similar to Britain with phone numbers being in the pattern “Dublin 123”. However, things diverged and became nuanced. As more phone lines were added, the “123” bit got longer. When direct dialling became possible, the “Dublin” (or where ever) bit changed to a number.
There was the problem that the phone system was related to the telegraph system, which was run by the post office, who ran telephone lines along railway company property. How much you paid for a phone call somewhat depended on where the railway lines were. This led to all sorts of oddness in remote areas, resulting in very long area codes and very short local phone numbers, e.g. +353-98765-43, with 98765 being the area code.
This has much improved, with most area codes now only having 1 to 3 digits. Most phone numbers are ‘area code + 5 to 7 digits’. When an area code is running out of numbers and 5-digit numbers are made longer, some people have the unfortunate habit of appending the extra digits to the area code instead of the individual number.
This is where the problem arises. You suggest three possible numbering formats. I think all three are unthinking and therefore inappropriate.
- +353-57-932-1234 and +353 57 932 1234 - a phone will understand it, but why are there two levels of area code? If I am visiting the country and I want to book a restaurant from my hotel room, do I dial “1234“, “932 1234“, or “57 932 1234“?
- +353579321234 - a phone will understand it, but a human will have difficulty working out what is country code, what is area code and what is phone number. As it isn’t split into blocks, it is difficult to read. Remember, there are no lower case numbers*, the equivalent of lower case letters, which give common words a shape and the brain can identify more quickly. Long numbers are difficult to read and / or identify as familiar.
I think the best way to do it is +353-98-7654321. Yeah, the last bit can be a block of 7 digits, but it beats the randomness and difficulty in comprehending the other formats.
There are oddities:
- Mobile numbers - in the format +353-8_-__ or 08_-__. The phone companies’ message minder services add an extra digit to these numbers.
- Phone company numbers - typically 4 digits for call centres and 6 digits for specific lines / services. I understand they have no area codes and all start with the digit 1.
- Non-geographic numbers - 1800 (freephone) and 0818 (standard rate).
- Premium rate numbers - 15__ (€€€€€€).
- Internet access numbers.
- Short numbers for SMS - 50___.
- A variety of special numbers 112 / 999 for emergencies, 116 numbers, etc.
These documents might be relevant:
Microsoft Word - ComReg03147.doc (old but has maps)
https://www.comreg.ie/publication/numbering-conditions-of-use-and-application-process-3 (appears current)
Numbering | Commission for Communications Regulation
* xkcd: Mavis Beacon