Closely related to "mapping UTC offsets to timezones": Mapping country calling codes to countries. Please just don't (if you're not going to handle NANP correctly).
Do Americans even know country calling codes exist?
In their defense, making the long distance prefix (1) the same as the country prefix (1) did not help spread that knowledge. I think most American know that something called "country calling code" exists, but probably couldn't tell you the code for the US. And I'd guess that most probably don't know that the +1 code includes Canada and most of the Caribbean islands.