There have been rumors about this for a while, and it is finally here! The Southwest iPhone app looks very similar to their mobile website and has all of the same functionality. The thing they have that is extra? The Ding! feature. This way you can find out about the specially-priced Ding! fares even when you are not at your computer. Cool!
For those of you who have other smartphones, Southwest says they are working on a solution for you, hopefully for release in 2010.