ConvertirLesAmr

http://www.hiteshagrawal.com/ffmpeg/converting-audiovideos-using-ffmpeg

http://www.convertfiles.com/

Converting AMR to MP3 using FFMPEG

ffmpeg -i audio1.amr -ar 22050 audio1.mp3

This will convert audio1.amr file to audio1.mp3 having audio rate 22.05 Kh