I started downloading the update at work, about 30 minutes before going home. Risky but I thought, what the hell. By home time, only about 200 out of 400 MB had been downloaded. I had to leave sharp to collect the kids and cannot dilly-dally, so I closed the Settings app, assuming that the download would be interrupted and I would either resume or start all over again at home. So you can imagine my surprise when I checked it at upon arriving home and found that the download had finished and my credit reduced by amount roughly equivalent to downloading 200 MB through mobile data.