I'm in the UK, and I don't think it's obvious what part of a mobile number is the "area code". With a phone number of 11 digits, how many digits form the area code? In a world where numbers aren't even connected to specific provider, the concept of area codes for mobile phones is broken. (Technically, my area code should start with +44 as well, as that's my area from an international point of view).
With landlines, you know which part of your number is the area code, because it has significance. If you call people living near you, you don't dial that code. This behaviour doesn't translate to mobiles.