A telephone number isn't really a number though, it's an address. This was probably more intuitive in the days of exchange names rather than STD codes, but we all know that they don't really count telephones, any more than house numbers count houses. Standard ways of formatting addresses are useful.
I'm reminded of barakta's prehistoric Mac, which is so old that you have to enter its IPv4 address as a single decimal (or hexadecimal) number, rather than the
dotted-quad representation we've become used to. Semantically, it's actually the binary representation that's important (for computers to make "this network"/"other network" distinctions, much like a telephone exchange has to), but humans are even worse at long binary numbers than they are at long decimals.
I suppose dotted-quad IPv4 addresses are a bit like the French approach of using 5 two-digit numbers for telephones - a standard format that makes the address clearer to humans for accurate transcription, but is only loosely related to the underlying system.
(CIDR/E164 analogy left as an exercise for the reader)