If it is a legacy Partner system, and the memory has been lost after a power failure, and the voicemail card is still functional, incoming calls will ring one time, the voicemail will answer, and since the Partner is no longer programmed, the VM will announce "Transferring to Receptionist" and transfer to Ext. 10.
As you are stating that Voicemail is not covering, it leads me to believe that the Partner programming is still there, and the Voicemail has suffered a hard drive failure when power returned. Can you dial Intercom 777 and reach the voicemail login prompt?
Please clarify exactly which system you are dealing with.