I like to tweak my keitai

3GP videos >> AVI

There is a lot of softwares and freewares able to convert 3GP keitai videos to other formats like AVI.
Those I am using is Front End Convert Drop, very simple and free.

Read 3GP videos or audio on Windows

Just install Media player classic and Quicktime Alternative (or just Quicktime if you like heavy interface without full screen...).
There is other ways but this one is my favorite.

AVI >> 3GP & MP3 >> 3GP

I am using 3GP_converter for the conversion.

For file transfering, I am using Chaku Edit if I want to upload the video/sound direct to the right video/sound SD directory (only AU / EZ web, W21CA / W31CA / W21T / W21SA / W31SA / W32SA / W33SA / W31S / A5406CA keitais).