Indeed, interfacing legacy GSM base stations is the primary use case. However, you can jsut as well use it to interface any other type of E1 equipment, like PBXs etc.
Would it be as simple as writing some high level software that interfaces with readily available libraries or would more possibly be necessary?
I’m fascinated by the opportunity that all of the legacy circuit switched(pardon me and my naïve googling if that’s the wrong term) hardware has left in critical places.