If you we able to use the fill 10mbit connection 24/7 for 30 days theoretically you would be able to get 25,920,000 MB's or 25.3125 GB in a 30 day month.
Keep in mind that just because you have a card that says it will process 10mbit it doesn't mean that you will. realistically, I wouldthink that the card would max out at about 22-23 GB a month. Then you have other variables too, like your upstream provider
I think that these numbers are correct, someone correct me if I am wrong.