I truly wonder who was the idiot who decided on the dialing scheme in use in Mexico.  Absolutely user-unfriendly, it means that a person roaming there doesn't actually know how to dial a number as the standard international form (country code + area/mobile code + number such as +52 55 5555-5555) just doesn't work.  To make matters worse, the number you dial to a mobile phone changes every time depending on where the caller and the receiver are.  Absolutely insane!

The details in Lee Iwan's blog.