This times a million.

Phone numbers in particular can be a horrid mess to deal with. Some decent libraries have come out to normalize them, but in general it remains difficult.

For example:

013811234 +88-1-3811234 3811234 0118813811234 008813811234

are all be the same number.

To hash them, you could naively just strip off the area codes and country codes, but that is only if you can know ahead of time they are indeed area or country codes. Some countries have 7 digit numbers, others have 9, some have 6, or even 5 digits. Sometimes you don't even know the country to apply these rules to.