I think that's what the VMX Locator at the bottom of each extension configuration page will do - perhaps not exactly the way you envision, but probably close enough. You could make a voicemail greeting that includes an instruction to press 0 for Operator, and some other digit to go to a different extension - I suppose you could even send them to an IVR or whatever (use a Misc Application to assign a dialable number to an IVR) and don't forget that from within an IVR there is an option to allow direct dialing of extensions.
So in its simplest form, you could record a voicemail message that says "Dial 0 for an operator, 1 to connect to another extension, or leave me a voicemail message now" - then if they press 1, send them to an extension you have associated with an IVR (using a Misc. Application) and in the IVR, be sure that "Enable Direct Dial" is checked. Record a suitable message for the IVR (assuming you aren't sending them back to your main IVR) that instructs them to dial the extension they want, and at a minimum include a t (timeout) destination in the IVR (which you can send to the operator extension). Also (optionally) check "Loop Before t-dest" in the IVR configuration, so they have plenty of time to dial the extension. So when they are in your voicemail, they'd dial 1, then the extension they want to reach (or 0 for an operator).
Try calling your extension from another internal extension and if it works from there, then it's probably a trunk configuration issue - your trunk may not be configured to allow incoming touch tones. In your trunk configuration, try adding these lines:
(Actually I think dtmf only affects outgoing and dtmfmode only affects incoming, but haven't looked it up to make sure, I just try those settings when I have this kind of issue). In an extreme situation you may have to add some "shim code" to set SIPDtmfMode to inband, an example of that as used with one particular provider is shown on this page - note line (3) in the custom context. But that is not usually necessary as long as your trunk settings are correct.
1) I do not actually use VMX Locator myself (ours is not that complex a system and we don't have an "operator" ), I just knew that it was available in FreePBX and might solve the OP's problem. What I wrote here was a best-guess effort at what I thought would work (sadly, the OP never replied to say if that solved his problem).
2) You're showing dial plan in your other post - I don't know if that's something you wrote or something FreePBX generated, but it's meaningless to me. I would need to know what you entered on the various FreePBX pages; I'm not about to decode someone else's dial plan, whether hand-written or generated by FreePBX.
3) Your comments in the other post might be helpful if I could read Spanish, but I can't. And I'm probably a bit too old to pick up a second language with any fluency.