If they cannot reach you by phone, they can send you a snail mail with some code printed on it that you have to enter into their admin interface. Admittedly the

If they cannot reach you by phone, they can send you a snail mail with some code printed on it that you have to enter into their admin interface. Admittedly they should tell you about that before you try to register (I discovered it after I already paid, but it just took a few days and all-in-one it wasn't too bad).