Well, the idea is to use the voicemail explorer feature as the tovoicemail.pl script converts the wav to stereo panning the legs of the call to the left and right. You should update the tovoicemail.pl script to convert the wav file to mono if you plan to listen to them from asterisk itself. I have not tried, but perhaps commenting the first two sox calls in the script will work (lines 69 and 70).
Best regards,
