I think it means the phone is turned off when it goes straight to voicemail. If it's no longer accepting calls, I figure someone didn't pay their bill, or your number has been blocked.
What does it mean when a call goes straight to voicemail? And also, what does it mean when you call someone and it says the phone no longer accepts calls? Does that mean it's no longer in service or just that it simply, doesn't accept calls :p