Board Thread:DC Universe Discussion/@comment-1635895-20121009211608/@comment-1038387-20121018103252

The latter.

Wonder Woman's flight is generally described as "gliding on air currents". It's a gift from Hermes, bestowed on her at her creation. As far as I know, it was an invention of Robert Kanigher in the late sixties, when he established her as being made of clay. Before that retcon, Diana had no different powers from her sisters, all her abilities were the result of years of training and study. She couldn't fly, but she used super leap. Perez kept the made of clay/"born" with powers thing after Crisis on Infinite Earths. I think they retconned flight away again in the DCnU.

She used the plane since the start. It's had different origins over the years - Amazonian tech, Alien tech, and in the movies, a combination of amazonian tech and a normal plane, and an alternate universe damaged cloaking field. As for why she uses a plane if she can fly, think of Crisis on Two Earths: "you drive a car". For long distance, the plane is better.