An extra first digit was added to UK phone numbers since the initial arrival of mobile phones, which now all start with 07. Before that there were no banded allocations so unused exchange codes were used. Hence some of the Wiki comments about renumbering ... [originally most landlines were alphabetically derived, such as the JE 0534, now with 1 added]
It's more complicated than your second post, and sometimes the next digit is required, for example 077000 is on the network Wire9, not in Jersey, and the 07911x isn't completely for Guernsey. And others are 075092 Jersey Telecom (used by Sim4travel) and 078297 Airtel Vodafone in Jersey
There are plenty of other 07 number ranges sub-divided and used for non-main networks, including allocations which might be for wi-fi use such as 079788 Truphone or the use is either ambiguous or defunct. Some have or had callthrough providers which the main networks have been in dispute with.
There is a huge
Excel file on the Ofcom website, which always takes me a while to find, as I forget to add it to browser Favourites. n.b. 070 aren't mobile numbers, and you need the A and B column for the so-called SABC + D/DE of the first few digits
... but the easiest way to check quickly is to enter the prefix on this site - if it says
(Insufficient digits or no match) then put the next digit as well -
Online CodeLook
Another which tends to be sometimes a bit less up to date
UK Telephone Code Locator - Telephone Codes, STD Codes
But those only give the original network's allocation range, and take no account of porting of individual numbers.
Why it ended up as haphazard as this, I suspect nobody knows ...
And
Quote:
Originally Posted by AndreA
Calls and SMS messages sent to island mobile numbers are not charged at the same rate as calls to UK mobile numbers
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UK landlines may have slightly differing tariffs to island landlines and mobiles. Most cheap calls providers make no distinction.
And main UK mobile networks may or may not include Guernsey Jersey and Isle of Man mobiles in their inclusive minutes. So if you're visiting with a roaming SIM it may cost UK friends a lot to ring you up. At the moment O2 Orange and Virgin seem to include most or all, T-mobile Vodafone and 3 exclude. Other mvno's probably vary. But this could change (O2 did), so it is worth checking