"We didn't specifically commit to adding D/FW," Kelly said, "but that certainly is in the spirit of what we agreed to do."
Overall, the partnership provides about $50 million a year in annual revenue, he said.
Cox said the ATA deal could be a first step toward bringing full Southwest service to D/FW.
"We are hopeful that over time, Southwest will see the wisdom and benefit of having the access to D/FW," he said.
And Wagner of American Airlines said it demonstrates that Southwest could choose to compete from the larger airport.
"This illustrates the fact that we do compete with low-cost carriers at D/FW, and there's more than enough room for competition here," he said.
But Kelly said the airline will remain at Love. "We still don't see any point to splitting our operation between the two airports," he said.
The service from D/FW becomes available for sale Jan. 3, and the flights will begin Jan. 11.
Stock in Southwest and American jumped Thursday amid optimism that the airline industry will recover next year.
Shares of Southwest (ticker: LUV) closed at $16.61, up 35 cents or about 2 percent. Shares of AMR Corp. ( AMR), American's parent company, jumped $1.83 per share, or 9 percent, to close at $21.44 per share.
Discount carrier AirTran Airways is adding its first new flights at Dallas/Fort Worth Airport in nearly 18 months, with nonstop service to Chicago Midway Airport.
A consultant hired by Dallas-Fort Worth International Airport says an expansion of nearby Love Field would lead to reduced flights and millions fewer passengers each year at DFW.
Round-trip fares on the eight flights will be $158 for tickets bought 14 days in advance and $258 for last-minute purchases.
Dallas Love Field could see traffic double or even triple if the Wright Amendment were repealed.