The North American Numbering Plan reserves 555-01 numbers for fictitious purposes. If you want an example Seattle number, for example,
+1 206 555 0100 -
+1 206 555 0199 would do.
In the United Kingdom, Ofcom, the regulator, has set aside numbers for this purpose. For example, if you want a Leeds number,
+44 113 496 0000 -
+44 113 496 0999 may be used.
I'm sure other countries will have similar things, but I doubt there's one consistent rule across all countries.
Australia lists ranges for premium, subscriber, toll free and local rate numbers.
Ireland - look for "drama use", which currently lists
020 91X XXXX as the only fictional range.
There's only one real standard for representing telephone numbers - E.164 - so from the perspective of storing a fictitious number, spaces don't matter -
+44 113 496 0000 is the same number as
+441134960000. But from the perspective of rendering a number to a user, there isn't a global standard, and even within a country there isn't usually a standard. In the US no one would give out their number as
+14255550123, they'd use
(425) 555-0123, or
425 555 0123. Within the UK, the 3-3-4 (
+44 113 496 0000) format is just one of them. Some numbers are 2-4-4 (
+44 20 7946 0000), and many numbers are a 4-6 pattern (
+44 1632 960999). See this Wikipedia article for more.