My host family has NTT + Biglobe. There is some concern my using the internet will increase their bill, but they aren't sure. The father was trying to tell me his email is unlimited usage and is a fixed rate per month, but the NTT portion may possibly vary according to usage, but he isn't. I agreed to pay any overage, and I want to ensure I won't get hit by a huge bill. So first of all, does that type of plan even exist?