OK, I did something stupid. I had a situation where calls would be directed to a end point (ext 100) if it was busy, it would forward to the second appearance on the phone (ext 101) then if RNA it would forward to MY OWN IVR SYSTEM (not VM on 3CX but another ext). When my first appearance (100) was busy, callers would experience ring tone (I could see the call ringing on my second appearance) then they would hear silence. In my trace I could see the call being transfered on RNA to my own IVR, but no voice. The problem was that I has set up the port range for external calls from 9000 to 9003. This was because of wanting to limit the number of ports I had to open in my firewall. But what happened is when 3CX ran out of RTP ports, it just did not open a port apparently, thus no voice. The bug is that there was no indication of this in the Server Status Log. It should have been in flashing red, bold with 15 stars and played an audio file that sounded like a car crashing. But it was silence, letting me tear my hair out for hours.