Here's a page from ATL Airport's website:

http://www.atlanta-airport.com/inter.../airlines.html

All airlines at Hartsfield-Jackson offering international service will use the international terminal complex. International flights for these carriers may be scheduled on either Concourse F or Concourse E.

In some cases, international flights may be scheduled on a domestic concourse. However, passengers on these flights will be required to check-in at the international terminal.

Airlines operating from the international terminal:

Air Canada (888) 247-2262
Air France (800) 237-2747
AirTran/Southwest (800) 247-8726
British Airways (800) 247-9297
Delta Air Lines (800) 221-1212
KLM Royal Dutch Airlines (800) 447-4747
Korean Air (800) 438-5000
Lufthansa German Airlines (800) 645-3880

Notice that it doesn't list Southwest as operating from terminal F.