It can mean different things. It is caused by the recipient (unknowingly) enabled call divert. When the phone is switched off, is out of service or is disconnected, you will hear the same message as you said. The problem here is that you can't know which error is happening so you should try calling again in a couple of minutes. If you hear the same, the phone is most probably switched off or disconnected. This can easily be fixed by asking the recipient phone to disable call divert, or set up a working voicemail system from Tele.