We use a Netphone Server which is Swyx, currently on version 13.
I don’t know how you organize your hotline so maybe you have to modify things a little bit but here is how we use it:
We have a dummy user for the hotline phone number (doesn’t need a Swyx licence) and in the call routing manager of this user we have a script that forwards the hotline calls to specific groups or the mailbox depending on the time etc. In the Start block of this call routing script we added a script that forwards the call information to Zammad.
I posted my script here
Maybe you have to adjust this for your use case but this should give you a good starting point to see how it works.