All the airlines are raising and lowering fares trying to keep up with one another.
Southwest raised domestic fares this week. A friend was booking a domestic ticket and the price of her flight jumped $150 in an hour. She did not book. Looked the next morning and the same fare went way down, she saved even more than the $150. Db just booked Spirit from Atlantic City to Ft Lauderdale for $107 round trip. Fare had been running $225+. It will cost me more than that in gas to drive from Georgia to Florida.
Monitor your fares regardless who you fly with, but know their change policies.
Southwest is still hoping to transition Air Tran international flights to Southwest by next spring. Let the games begin!