Mobile Phone - Oz
Answer
My calls don't divert to voicemail when I'm on the phone, out of range or if the phone is switched off.
This sometimes happens when changes have been made to diversions of calls. Its an easy one to fix.

Turn on your phone, key in **004*321# and hit the send/call button.

This should reset all diverts to voicemail as:-

Divert to voicemail when on the phone

Divert to voicemail when out of range

Divert to voicemail when phone is switched off