I typically don't CFNA any of the extensions to voicemail. I set the DRT to prime (Y), make prime set the vmail DN. All calls going through auto attendant will end up in voicemail after ringing the extension according to the DRT delay timer (typically 4 rings). Fo calls that are answered live, I train the users to transfer callers directly to voicemail when desired either by a pre-programmed button or f986.