In my country (North Carolina) I use unix time YYYY-MM-DD and only need the other format for such things as insurance billing.
"Postal code" would likely work anywhere (even in the USA) but would be easily solved by a xml() translation field based on language.
If we started adding the international calling number aka 01 for the USA, the problem should be easier for all countries. Display is usually only how the numbers are routinely formatted. I think it would take 12 digits to make sure that all country codes would work? This may take a little extra research.