If you have Inbound dialing, you can create extensions for your inbound phone number.

Firstly, go to Settings> Phone Dialer & Call Queue Lists> User Groups
Set up the User Groups to determine which agents will receive which calls.

Secondly, go to the IVR tab
Create IVR menu, name it and select the Greeting to use (Upload mp3s or create a text to voice message on the Greetings tab)
Determine the selections.

Thirdly, add the extensions. They can go to an individual user, to a ring group or to an external phone number.