What is required of a user to retrieve voice mail once they are notified of a new message by Cisco Unity Connection Message notification on their mobile phone?

A password in Unity Connection is used for web-based access such as the Personal Communications Assistant, not for phone-based voicemail retrieval.

Cisco Unity Connection uses PIN-based authentication to verify a subscriber's identity when they call in to retrieve messages, including when responding to a mobile phone notification. The PIN is the standard credential for voicemail access and is required regardless of how the user was alerted to a new message.

The user ID alone is not sufficient for authentication - it identifies the user but does not verify their identity without the accompanying PIN.

The user extension is used to route calls to a mailbox but is not an authentication credential for retrieving messages.

FAC (Forced Authorization Code) is a CUCM feature used to authorize specific call types and has no role in voicemail authentication.