VOS3000 2.1.9.07 new version upgrade guide covers SIP improvements, billing precision, security, ASR failover, Web API, IVR, and CentOS 7 for VoIP operators.
VOS3000 Call Failed Announcement: Easy IVR Voice Prompt Setup
VOS3000 call failed announcement plays IVR voice prompts when calls fail. Configure the IVR module to announce busy, unreachable, and other failure reasons to callers.