I wonder how much they took people still using their cell phone number from an area code they no longer live in. Would be cool to see an interactive version of this map too.
I'm not seeing anything that indicates whether they differentiated between area codes/numbers and geographical locations of the caller and callee.
I suspect, however, area code/number analysis would be easier. Example: Alice lives in Atlanta, but kept her St. Louis number so that her mom with a land line can call her without long distance fees. So when Alice calls mom from Atlanta, it's a call from Atlanta. Bob lives in St. Louis but travels to Atlanta on business. When Bob calls his wife in St. Louis on his St. Louis number from Atlanta, should that be a call from Atlanta back to St. Louis?
I suspect, however, area code/number analysis would be easier. Example: Alice lives in Atlanta, but kept her St. Louis number so that her mom with a land line can call her without long distance fees. So when Alice calls mom from Atlanta, it's a call from Atlanta. Bob lives in St. Louis but travels to Atlanta on business. When Bob calls his wife in St. Louis on his St. Louis number from Atlanta, should that be a call from Atlanta back to St. Louis?