I've noticed that this happens about once a month and lasts for a few days. I think it has to do with maintenance, during this time you might notice your Internet dropping to a 0bps transfer rate also. Still haven't figured out what causes it for sure, they don't seem to know at the Vodafone stores on base, pretty much just deny that it happens. That's customer service in the Naples area though, have come to not expect much more.