Today I had the displeasure of having to figure out how to retrieve and convert voicemail files from some old Mitel 3300 controllers.

Thanks to this forum post which pointed me in the right direction.

1. Connect via FTP using a proper FTP client like FileZilla, to the 3300’s IP address
2. Navigate to /vmail/d/vm/grp/<extension>
3. Grab the relevant file. They’re all G.711 U-Law format RAW audio files
4. Grab SoX – https://sourceforge.net/projects/sox/, and extract it somewhere
5. Run the following command:

sox.exe --channels 1 --type raw --rate 8000 -e u-law -v 1 -D <inputfile> outputfile.wav