VoIP Specialist Needed for Ringless Voicemail

I'm looking for a VoIP engineer who can implement a two-call method: the first call should ring for no more than half a ring, and the second call should go directly to voicemail.
I've already set up this two-call method on FreeSWITCH, but I can't get the second call to not ring at the destination phone.
I’d love to discuss how we can fix this.

Key Responsibilities:
- Implementing Ringless Voicemail on our existing system
- Enhancing our customer feedback collection process
- Ensuring optimal performance of the VoIP system

Ideal Candidate:
The ideal freelancer for this project would have extensive experience in VoIP, specifically with Ringless Voicemail. They should also have a deep understanding of customer service enhancement techniques and how to implement them using VoIP technology.