Are there any converters around that allow conversion of FLV/AVI/MP4 videos to mobile 3GP format? Preferably GUI based, but I haven't managed to find one yet.
WinFF is a GUI for the command line video converter, FFMPEG. It will convert most any video file that FFmpeg will convert. WinFF does multiple files in multiple formats at one time. You can for example convert mpeg's, flv's, and mov's, all into avi's all at once. WinFF is available for Windows 95, 98 , ME, NT, XP, VISTA, and Debian, Ubuntu, Redhat based GNU/Linux distributions.
WinFF is open source and cross platform written in Free Pascal and Lazarus. WinFF is published under the GNU public license. WinFF is published without any warranty or suitability for any purpose.1
To Install WinFF For Ubuntu
Now and then when I need to convert files with no fuss, I use ConvertFiles.com online application.
It does what you want with a simple graphical interface, plus it's easy and free.
You could try mobile media converter it has always worked for me you can get it here it has a good User Interface and it has a vast array of presets to convert to.