If you are serious about it I would say Business Management and contact them now. Try and do a job shadow, internship or something else like that. The companies can vary on how they go about their sales tactics and can even vary from office to office. Drop @AdamJGray a line and show your interest.
I had looked into it a couple of times but I don't like being sold to and when someone tells me no I wouldn't have been pushy and would have just told them to have a nice day....not a great attribute for a salesmen.
Oh yeah. Management would be good as well as Marketing.