I have 3GA files which were produced by a mobile phone.
To convert 3GA files into MP3 files, I use:
$ avconv -b 256k -i OneOfThe3gaFilesIRecorded.3ga PreferredMP3.mp3
For example, a 3GA file of 595KB can become an MP3 file of about 1.7MB. I like MP3 files because many devices can play them.