A system for dialing numbers on a phone that requires you to dial the area code for every call you make. It makes sense for those in large cities, where one's next door neighbor may be in a different area code. Making the area code non-optional has several advantages:
  • never again hearing the lamest pre-recorded message ever invented, "I'm sorry, a 1 is not required when dialing this number."
  • not worrying about whether the person who gave you their phone number didn't give you the area code because they incorrectly thought you were in the same one.
  • not having to change your dialing habits when you're at work in a different area code

In short, it's definitely a feature in cities with multiple area codes. Orthogonal systems are good. It's probably a bug in places where a single area code covers tens of thousands of square kilometers.