Converting movies for my phone

I've been spending the morning (and until now, in fact) playing with a nifty application named 3GP_converter, which uses ffmpeg and such to translate movies into a version readable by my sagem mobile. I've managed to get the video working beautifully, but the sound still gets lost in translation.
Pity. Anyway, I will try later on if I can find some hack able to do it. with Quicktime I can export the file, but most of the settings which should work (H.263 for the video, AMR-narrowband for audio) results in movies which even on the pc stop playing after a few seconds. pants!