When I lived in the South, I found that most servers would ask "together or separate checks?" When I moved up North, I've found that 99% presume it's just one check. Even when in college in the Boston area, I don't remember a single occasion where the server automatically split the check for us without us having to ask. Granted, when I have explicitly asked either before or after the meal to split the bill, 99% of the time, there isn't a problem at all.