I recently was in need of converting a video to 3GP format so I was able to play it on my HTC tp, Now there are a lot of programs for doing this in a windows environment and I even have one however I wanted to find a way to do it running Ubuntu. I was able to do it with Pitivi This program actually does a whole lot and I was very impressed with it. I was able to load it from Synaptic package manager.
This video is all ready in 3GP format but I only loaded it for representation.