Originally posted by mcmbenjamin
I remember you telling me about the 020 for London and 077 for mobile phones but my question is why the zero? Well the best I can come up with is that the zero is a throw back to the old telephone systems.
Wikipedia says the zero 'of a telephone number (called the trunk prefix) is not properly considered part of the area code but is, rather, the national long distance calling prefix, and thus (for example) 023 is a "two-digit" area code.'
As you rightly mention, it's the "trunk prefix" number - or perhaps a better description is "national dialling code". It's the digit that indicates to the local exchange that you're dialling a number that isn't in your local area - just like when making an international call from the UK, you dial 00 to indicate to the exchange that you're dialling an international number.
Technically, the 0 isn't part of the area code at all, but convention would dictate that you tell someone that the area code includes the national dialling code - after all, if they have to dial the area code, it's obvious that they're not dialling locally (when you wouldn't need the area code)

In suppose it is a throwback to the pre-digital exchange and what the exchange would "expect" next in a sequence of numbers - though I don't know if the digital exchange could cope with dropping it. Actually "cope" is probably the wrong word.....it'd probably need a heck of a reprogramming job.
If you have chronic insomnia, have a look at
this 1997 draft of the Consultation on Revisions to the National Numbering Convention (PSTN) or have a look through
Ofcom's numbering policyAnd now, without further ado (I hope), we return you to the original topic of this thread....
Cheers
Michael