I sell these products. I wish I didn't.
I have sold 15+ Magic jacks, and had all 15 new in box products returned because they 'did not work.' I did not test further then that, I took the customers at face value.
That is all my experience with them. I pulled them off my shelves and stopped carrying them. Other stores have told me they sell them fine. I stopped caring. I only sell them if someone asks for it directly, and then I tell them my experience, and that I will not be taking a refund on it.