I would think/hope that most video editing programs can work with .3gp. If you're using Windows, Movie Maker is free and should be able to do this.
Have you done any searching yet?
This actually looks like it might be of use to you »forum.videohelp.com/thre ··· ROTATION
and here is my Google search »www.google.com/#hl=en&ou ··· &bih=651
So it looks like you may have to convert it to AVI first, and then use Movie Maker to rotate it.--
Rule #62: Don't take yourself so damn seriously!