Not every aspect of this is easy, true, but that's no reason not to tackle the ones that are. It's trivial to simply not require a state or a postcode or try to

Not every aspect of this is easy, true, but that's no reason not to tackle the ones that are. It's trivial to simply not require a state or a postcode or try to verify a phone no if the user selects a country other than the US. There should be a library for this. We have libraries that can handle the insanely capricious details of DST for all countries and subnational entities on the planet; we should have no problem providing one list of states and two regular expressions per nation. (I know it's more or less impossible to reliably catch (e.g.) invalid UK postcodes, but we wouldn't have to. We'd mainly want to catch obvious typos without making things needlessly hard for customers overseas.)