Hooked up my rarely used Ipod to my mobile hotspot the other day just to run a couple speed tests before bed. Didn't download anything or do anything else. Wake up in the morning with a warning that I'm almost out of my hotspot data. Somehow it used up 2 gigs while I was sleeping. This is on an 8 gb Ipod with almost nothing on it, definitely no where near 2 gb. CS says they can't do anything about it. This is ridiculous. I finally get the hotspot after holding out to change plans for 6 months and its used up already after only a few days into my billing cycle. All they could tell me was to make sure its turned off when not in use.
So... fair warning to everyone else, make sure you have it turned off if not being used.