It's possible to attach a voicemail message to a missed call so that it will look like that:
In order to get the voicemail Asterisk must be configured to use Minivm applications. Below is an example of a dialplan:
[odoo-from-internal] ; context for internal users
exten => _XXX,1,Set(CHANNEL(hangup_handler_push)=cleanup,s,1(args))
exten => _XXX,n,MinivmGreet(${EXTEN}@default)
exten => _XXX,n,MinivmRecord(${EXTEN}@default)
[cleanup]
exten => s,1,ExecIf($["${MVM_FILENAME}" != ""]?Goto(del,1))
exten => s,2,Return
exten => del,1,System((sleep 5 && rm ${MVM_FILENAME} && rm ${MVM_FILENAME}.WAV)&)
exten => del,2,Return
In the above example we greet the caller with the default message. After the message is recorded call is hangup and voicemail file is deleted after 5 seconds delay. We use this delay so that Odoo will have enough time to get the recording.
For more information read:
Asterisk MinivmRecord app.
Asterisk MinivmGreep app.
Please note that Asterisk VoiceMail app is not supported as it requires static mailboxes configuration. And Minivm app does not require any configuration for user accounts.