This site about North American telephone area codes has a number of maps showing the current and historical area code assignments. With new area codes being added or overlaid all the time, it’s hard to keep up. But here’s a map of the area codes in 2003, plus maps of the codes as they were assigned in 1947 and as they were in the 1970s. There’s also a map of the current codes for the Caribbean — they’re not all just 809 any more. (Thanks, Huw.)