We upgraded our CUCM environment from 10.5.2 to 12.5.1 recently and immediately faced what TAC is investigating as a potential bug. Our situation is we have SIP trunks to the PSTN that include MTP. Our integration with Unity Connection is SCCP. After the upgrade to CUCM 12.5, we no longer were getting DTMF into Unity Connection. We aren't the only ones that are experiencing the issue. TAC is investigating it and I don't see any bug yet that's been posted about it.
To get around the issue, they suggested we move our CUC integration to SIP instead of SCCP. We did that and the DTMF started to work.... BUT a feature I have been using since about 2001 stopped working. We setup voice mail profiles in CUCM to tie lines to specific voice mail boxes. That has the benefit of sending callers to specific voice mail boxes when they call a particular DN. It also makes it easy to retrieve voice mail from a particular box from a particular line on the phone. For example, we setup a second line a phone that goes into a hunt group (which, if not answered go to a shared voice mail box). With the old configuration those that wanted to retrieve voice mail from that box would press that line appearance on the phone, then press the voice mail button, enter the PIN and they can listen to the voice mail. That doesn't work with SIP integration. I had to enter alternate extensions in Unity Connection (which is limited to 9 extensions) to get the same functionality. NOT a very clean way to solve the problem, especially because for some of these we would need many more than 9 alternate extensions.
I am hoping that the SCCP integration with CUC is fixed soon.
I would encourage you not to revert to SCCP as it has a questionable future.
Let’s think about how to solve this with SIP. I have read your post multiple times and will admit that I don’t exactly follow - pardon if I miss the mark a bit.
First idea: since the workflow sounds heavily TUI-oriented, have you looked at Dispatch Messaging to a DL from a Call Handler instead? This has the advantage of depositing the VM into each person’s existing mailbox (ie eliminates the shared mailbox), gets MWI at scale, allows normal sign-in from their existing DN, AND recalls the message from all other mailboxes once someone accepts it. Think of it sort of like accepting ownership of a ticket. The only drawback to this feature is that you must use the TUI to accept the message.
Another option is to configure a shared mailbox in MS Exchange, keep the CUC shared mailbox, enable Single Inbox to the Exchange mailbox, and have users work from Outlook. You could optionally add ViewMail to the equation if they wanted to playback via phone.
According to the bug, there's an ES where it is fixed but that's not available yet. That is, if you're talking about the DTMF issue. If you're wondering about the Voicemail Profile issue, it has been that way forever and right now there's no plans to change it. If you would like to see SIP integration with Unity have feature parity with SCCP integration, talk to your account team and see if they can escalate the request.