At the moment, the World Phone module contains its own hardcoded mapping from two-character country codes (ISO 3166 codes, like "US", "CA", and "UK") to country short names (like "United States of America", "Canada", and "United Kingdom"), as well as an API for looking up countries. That's because, when World Phone was written, there was no standard resource in Drupal for obtaining a map from ISO 3166 codes to country short names.

But now there is: The Country codes API module. I think this module should incorporate Country codes API as a dependency and remove its own API for ISO 3166 codes.