Yes, An extension calling can get the VM, also if setting the call flow to go directly to VM that works too, and if the extension is unregistered it hits voicemail also. Any other way it just says Not Answered in the Activity Log, hangs up.
I think the thing is with the DID number being seen as an extension by the system, I did not have the issue previously it's only on that new install. It's the only DID setup, all very basic setup with one extension, created a second 101 and it behaves exactly the same. Cannot reach extension's VM from the DID but it rings and everything.
I think usually it should say "person at extension 100" is not available instead of playing the DID number? It's what I find curious. It's like the DID itself should have VMail configured but that's not the way 3CX seems to work.