The busy tone sounds when a Cisco Unity pilot number is called from an external number.
The Cisco Unity is not configured to allow access to the Cisco Unity mailbox with the user ID and password. It is not acceptable to press star * so that the Cisco Unity switches to the user ID and password prompt.
In order to resolve this issue, create a new rule for Call Routing on the Cisco Unity so that it prompts for the user ID and password instead of the name, which is the default.
In order to create a new routing rule, complete these steps:
Choose Call Routing > Direct Calls.
Create the new rule with the option of Send call to: Sign-in and put it on the second order.