^ if i am not mistaken, .3gp is just a new filename for quicktime .mov files. in other words, you should be able to simply take a quicktime file and rename it to .3gp, then it should play just fine on your phone. not sure about the resolution and/or scaling...
this trick works on many phones that support custom .3gp ringtones, where you take a standard .mp3 file and rename it to .3gp without any need to transcode the data.