What is interesting about this, and sort of tangentially how I found it out, is this means there are ranges of number that (I think anyway) can be dialled on TWO international dialling prefixes.

+44 28 8728 7000
or
+353 48 8728 7000

I think this works, or mostly works, and I'm not sure it was part of the intended design.

But it certainly seems to work, in at least some circumstances.