I’ve recorded a track using OSMTracker for Android with some 3gpp audio notes. When I try to open them in JOSM I get the message
INFO: Opening URL: file:/full/path/to/file.3gpp
in terminal, but I don’t hear anything. I use Arch Linux with i3wm and xdg-open opens the files correctly.
I remember having had that trouble years ago!
Try an internet search for “JOSM 3gpp” or similar, and you fill find many hits with same problem and maybe a workaround.
Here it’s said that it should work out-of-the-box with the default player, but it doesn’t.