Custom voicemail message can set in two ways:
Recorded as a busy or unavailable message with a phone handset by connecting to the voicemail pickup for the relevant extension, selecting 0 for voicemail options and then select 1 for unavailable or 2 for busy message recording.
From a file, which has to be converted (using e.g. Audacity - format: alaw, 8Khz, mono) into alaw format and renamed to “unavail.alaw” or “busy.alaw” and copied into “/var/spool/asterisk/voicemail/default/XXX/” directory on PBX (XXX is the extension number that custom voicemail message should be used for, ‘default’ represents the company on multi-company systems).
How to convert file using Audacity:
a) Open file and go to Tracks/Resample. Select new sample rate: 8000, Select project Rate in left bottom corner to 8000.
b) Go to File/Export Audio, select “other uncompressed files”. In options select Header: RAW, Encoding: A-Law.
c) Save file with .alaw suffix.
How to verify if exported file is correct using Audacity:
a) Got to File/import/Raw Data.
b) Select filename.alaw.
c) You will be prompted for file parameters. Select Encoding: A-Law, Byte order: Little-endian, Channels: Mono, Sample rate: 8000. Click on “Import”
d) Play file, you should hear audio.