BlkBear
Just makes it easier to read the numbers for most people. You don't need the hyphens to dial the numbers.
Also is a hold over when numbers were area code, Prefix and the rest would tell you the exchange, where in the city a particular number would be. Now with number porting, it's pretty much just a number attached to an account on any cell carrier.
spacemissing
Ask a phone company.
Murzy
Easier to read the numbers.