We have some videos recorded using our cell phone and it was in Portrait setting. You know what I mean.
I was also looking for a utility to rotate my 3GP videos (I have a mytouch4G).
I found this free utility "freevideoflipandrotate" from DVDVideoSoft.com
Link to FreeVideoFlipAndRotate
Just some notes:
1. During the install, it has an option that ask if you want to "...Plasmo web search as my homepage..." - for me I unchecked this.
2. Before you use this utility, I suggest you convert your video to avi, or mp4. When I tried rotating my 3GP, it worked, but it changed the speed of the video. I used "Format Factory" to convert my videos first. It's also a free tool.
Rotating a 3GP video directly to a rotated AVI video, notice the speed...
Here is how the video turned out... not too bad.