What is enhanced voicemail?
When configuring DDIs or Auto Attendants to point to users, you get an option for "Enable Enhanced Voicemail".
Regular voicemail (referred to as "Residential Voicemail") simply prompts the caller to leave a message then hangs up. Enhanced voicemail gives the caller a couple more options in routing their call.
Firstly it will give the user the option to dial an extension number to get through to someone else.
Secondly you can configure an operator which the caller can opt to be transferred to.
The operator settings can be found under a user's voicemail tab: