musiconhold.conf

[default]
mode=files
directory=/var/lib/asterisk/mohmp3


(tried also mode=quietmp3)

make clean autoload:

/bin/cp -f format_mp3.so /usr/lib/asterisk/modules
asterisk -rx "load format_mp3.so"
 Loaded /usr/lib/asterisk/modules/format_mp3.so => (MP3 format [Any rate but 8000hz mono optimal])
  == Registered file format mp3, extension(s) mp3


on debug

 -- Created MeetMe conference 1023 for conference '111'
    -- Playing 'conf-onlyperson' (language 'en')
    -- Started music on hold, class 'default', on channel 'SIP/10.90.1.2-0819bbc0'
    -- Stopped music on hold on SIP/10.90.1.2-0819bbc0