Hey guy, this probably wont be helpful to you at all but it came to mind when reading your post. Several months ago when I was in the middle of moving I was using tether ALOT. (I normally use between 3-4GB of data per month) I had my home internet turned off and it was going to be three weeks before Cox was going to be able to get us online at the new house. I was not downloading 700mb files at a time by any means but it was the only way I could get my family online. Between myself my wife and our kids we racked up 9.7GB of data on my line that month. I didn't think twice about it since my plan is "unlimited" right? Got a call about a week later from Verizon confronting me about this, kind of caught me off guard. They even knew the exact amount of data that was transferred from PC vs what was transferred to my phone. Apparently they use different packet sizes or something? Hell I don't know how they can tell I'm just guessing. Anyway I explained the situation to them (I played the dumb card and acted like I had no idea that I wasn't supposed to do that.) They let me off the hook but informed me how expensive this would have been had they actually pursued it.
I'm not trying to tell you what to do or what to download but I am saying watch out how much data you use, especially if you aren't the one paying the bill. I don't know if they give everyone a free warning. Just saying they apparently do keep tabs on things. Sorry for such a long post. Good luck!