All of the video recordings in my phone are in .3gp, so I must convert them to something else before I can edit them in iMovie.  I wrote a script to convert all of the .3gp files in a folder to .mp4. It uses ffmpeg

Here is the gist on github

You run it by navigating to the folder with all of your movie files in it and typing

./mobile_movie_convert.sh

and all of the movies will be converted, leaving the originals. The converted movies will have the same name as the original but with an .mp4 extension. So test.3gp as input will produce test.mp4 as output.