A long, long time ago I used to have a Samsung Galaxy. I used to get a ton of voicemail, and I learned later on that I could download the voicemail locally to the phone. It would be stored as an AMR and I didn’t really like that.
I needed to convert the AMR files to MP3 files, so ffmpeg came to the solution:
ffmpeg -i "source.amr" -vn -ar 44100 -ac 1 -ab 128k -f mp3 "destination.mp3"