That is a phone model and not system. the hipath 3000 can have an slt- a/b port changed to be a music on hold port, the newer unify system does have internal storage but not for large files, still use an external player on a analogue port or you can get a daughter card to connect where the extra Siemens dongle with internal music on it plugged in

I presume the 4k does as well but, I don't know that too well

“I have not failed. I've just found 10,000 ways that won't work.”